A

Fake NP

standard input/output

 s,  MB     Submit  Add to favourites     x3673

B

-palindrome

standard input/output

 s,  MB     Submit  Add to favourites     x3760

C

Find Amir

standard input/output

 s,  MB     Submit  Add to favourites     x3503

D

Minimum number of steps

standard input/output

 s,  MB     Submit  Add to favourites     x2242

E

Ice cream coloring

standard input/output

 s,  MB     Submit  Add to favourites     x142

F

Expected diameter of a tree

standard input/output

 s,  MB     Submit  Add to favourites     x28

//By SiriusRen

#include <map>

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

map<int,int>mp,remp;

int l,r;

int main(){

	scanf("%d%d",&l,&r);

	if(l==r){

		printf("%d\n",l);

	}

	else{

		puts("2");

	}

}

//By SiriusRen

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

int n,a[200050];

int main(){

	scanf("%d",&n);

	a[1]=0,a[2]=1;

	for(int i=3;i<=n;i++){

		if(a[i-2]==0)a[i]=1;

		else a[i]=0;

	}

	for(int i=1;i<=n;i++)printf("%c",a[i]+'a');

}

//By SiriusRen

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

int n;

int main(){

	scanf("%d",&n);

	printf("%d\n",n/2-1+(n%2));

}

//By SiriusRen

#include <cstdio>

#include <cstring>

using namespace std;

const int N=1000050,p=1000000007;

char s[N];

int n,ans,res;

int main(){

	scanf("%s",s+1),n=strlen(s+1);

	for(int i=n;i;i--)

		if(s[i]=='b')res=(res+1)%p;

		else (ans+=res)%=p,(res+=res)%=p;

	printf("%d\n",ans);

}

//By SiriusRen

#include<bits/stdc++.h>

#define N 300005

using namespace std;

vector<int> G[N],E[N];

int n,m,ans,col[N],cnt,vis[N];

void dfs(int t,int fa){

	int i,cnt=1;

	for(i=0;i<E[t].size();i++)

		if(col[E[t][i]]) vis[col[E[t][i]]]=t;

	for(i=0;i<E[t].size();i++)

		if(!col[E[t][i]]){

			while(vis[cnt]==t) cnt++;

			vis[cnt]=t,col[E[t][i]]=cnt;

		}

	for(i=0;i<G[t].size();i++)

		if(G[t][i]!=fa)dfs(G[t][i],t);

}

int main()

{

	int i,x,y;

	scanf("%d %d",&n,&m);

	for(i=1;i<=n;i++){

		scanf("%d",&x),ans=max(ans,x);

		while(x--)scanf("%d",&y),E[i].push_back(y);

	}

	for(i=1;i<n;i++)scanf("%d%d",&x,&y),G[x].push_back(y),G[y].push_back(x);

	dfs(1,0);

	printf("%d\n",max(ans,1));

	for(i=1;i<=m;i++)printf("%d ",max(col[i],1));

	return 0;

}

//By SiriusRen

#include <set>

#include <vector>

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

const int N=200050;

vector<int>vec[N],dis[N],sum[N];

struct Node{int x,y;double ans;}JY;

bool operator<(Node a,Node b){if(a.x!=b.x)return a.x<b.x;return a.y<b.y;}

set<Node>s;set<Node>::iterator it;

int n,m,q,first[N],nxt[N],v[N],w[N],tot,root,xx,yy,vis[N];

int maxx[N][2],rec[N][2],f[N],Root[N],vv[N],fi,flag,size[N];

void add(int x,int y){w[tot]=1,v[tot]=y,nxt[tot]=first[x],first[x]=tot++;}

int find(int x){return  x==f[x]?x:f[x]=find(f[x]);}

void get_dia(int x,int fa){

	rec[x][0]=rec[x][1]=x;

	for(int i=first[x];~i;i=nxt[i])if(v[i]!=fa){

		get_dia(v[i],x);

		if(maxx[v[i]][0]+w[i]>maxx[x][0])

			maxx[x][1]=maxx[x][0],rec[x][1]=rec[x][0],

			maxx[x][0]=maxx[v[i]][0]+w[i],rec[x][0]=rec[v[i]][0];

		else if(maxx[v[i]][0]+w[i]>maxx[x][1])

			maxx[x][1]=maxx[v[i]][0]+w[i],rec[x][1]=rec[v[i]][0];

	}if(maxx[x][0]+maxx[x][1]>maxx[root][0]+maxx[root][1])root=x;

}

void DFS(int x,int fa,int deep){

	vv[x]=max(vv[x],deep);

	if(flag)vec[fi].push_back(vv[x]),size[fi]++;

	for(int i=first[x];~i;i=nxt[i])if(v[i]!=fa){

		DFS(v[i],x,deep+w[i]);

	}

}

int main(){

	memset(first,-1,sizeof(first));

	scanf("%d%d%d",&n,&m,&q);

	for(int i=1;i<=n;i++)f[i]=i;

	for(int i=1;i<=m;i++)

		scanf("%d%d",&xx,&yy),add(xx,yy),add(yy,xx),f[find(xx)]=find(yy);

	for(int i=1;i<=n;i++){

		fi=find(i);

		if(!rec[fi][0]){

			root=flag=0,get_dia(i,0),Root[fi]=root;

			DFS(rec[root][0],0,0),flag=1,DFS(rec[root][1],0,0);

		}

	}

	for(int i=1;i<=n;i++){

		fi=find(i);

		if(!vis[fi]){

			vis[fi]=1;

			dis[fi].resize(size[fi]+1),sum[fi].resize(size[fi]+1);

			for(int j=0;j<vec[fi].size();j++)

				dis[fi][vec[fi][j]]++,sum[fi][vec[fi][j]]+=vec[fi][j];

			for(int j=size[fi]-1;j>=0;j--)

				dis[fi][j]+=dis[fi][j+1],sum[fi][j]+=sum[fi][j+1];

		}

	}

	while(q--){

		scanf("%d%d",&xx,&yy);

		int fx=find(xx),fy=find(yy);

		if(fx==fy){puts("-1");continue;}

		if(vec[fx].size()>vec[fy].size())swap(xx,yy),swap(fx,fy);

		JY.x=fx,JY.y=fy;

		if((it=s.find(JY))!=s.end()){printf("%.10lf\n",it->ans);continue;}

		int dis1=maxx[Root[fx]][0]+maxx[Root[fx]][1];

		int dis2=maxx[Root[fy]][0]+maxx[Root[fy]][1];

		int Dis=max(dis1,dis2);

		long long ans=0;

		for(int i=0;i<vec[fx].size();i++){

			ans+=sum[fy][Dis-vec[fx][i]]+1ll*dis[fy][Dis-vec[fx][i]]*(vec[fx][i]+1);

			ans+=1ll*Dis*(size[fy]-dis[fy][Dis-vec[fx][i]]);

		}

		JY.ans=(double)ans/size[fx]/size[fy],s.insert(JY);

		printf("%.10lf\n",(double)ans/size[fx]/size[fy]);

	}

//	for(int i=1;i<=n;i++)printf("%d ",vv[i]);

}