//#include<bits/stdc++.h>

#include<iostream>

#include<cstdio>

#include<ctime>

#include<cctype>

#include<queue>

#include<deque>

#include<stack>

#include<iostream>

#include<iomanip>

#include<cstdio>

#include<cstring>

#include<string>

#include<ctime>

#include<cmath>

#include<cctype>

#include<cstdlib>

#include<queue>

#include<deque>

#include<stack>

#include<vector>

#include<algorithm>

#include<utility>

#include<bitset>

#include<set>

#include<map>

#define ll long long

#define db double

#define INF 1000000001

#define ldb long double

#define pb push_back

#define put_(x) printf("%d ",x);

#define get(x) x=read()

#define gt(x) scanf("%d",&x)

#define gi(x) scanf("%lf",&x)

#define put(x) printf("%d\n",x)

#define putl(x) printf("%lld\n",x)

#define rep(p,n,i) for(RE int i=p;i<=n;++i)

#define go(x) for(int i=lin[x],tn=ver[i];i;tn=ver[i=nex[i]])

#define fep(n,p,i) for(RE int i=n;i>=p;--i)

#define vep(p,n,i) for(RE int i=p;i<n;++i)

#define pii pair<int,int>

#define mk make_pair

#define RE register

#define P 1000000007ll

#define gf(x) scanf("%lf",&x)

#define pf(x) ((x)*(x))

#define uint unsigned long long

#define ui unsigned

#define EPS 1e-4

#define sq sqrt

#define S second

#define F first

using namespace std;

char *fs,*ft,buf[1<<15];

inline char gc()

{

	return (fs==ft&&(ft=(fs=buf)+fread(buf,1,1<<15,stdin),fs==ft))?0:*fs++;

}

inline int read()

{

	RE int x=0,f=1;RE char ch=gc();

	while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=gc();}

	while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=gc();}

	return x*f;

}

const int MAXN=100010;

int n,m,Q,cnt,top,mx;

vector<ll>G[MAXN],c[MAXN];

int g[MAXN],f[MAXN],w[MAXN],s[MAXN],id[MAXN],vis[MAXN];

int lin[MAXN],ver[MAXN<<1],nex[MAXN<<1],len;

map<int,ll>H[MAXN];

inline void add(int x,int y)

{

	ver[++len]=y;nex[len]=lin[x];lin[x]=len;

	ver[++len]=x;nex[len]=lin[y];lin[y]=len;

}

inline void dfs(int x,int fa)

{

	vis[x]=cnt;

	go(x)if(tn!=fa)

	{

		dfs(tn,x);

		mx=max(mx,f[x]+f[tn]+1);

		if(f[tn]+1>f[x])

		{

			g[x]=f[x];

			f[x]=f[tn]+1;

			id[x]=tn;

		}

		else g[x]=max(g[x],f[tn]+1);

	}

}

inline void dp(int x,int fa)

{

	s[++top]=f[x];

	go(x)if(tn!=fa)

	{

		if(id[x]!=tn)

		{

			if(f[x]+1>f[tn])

			{

				g[tn]=f[tn];

				f[tn]=f[x]+1;

				id[tn]=x;

			}

			else g[tn]=max(g[tn],f[x]+1);

		}

		else

		{

			if(g[x]+1>f[tn])

			{

				g[tn]=f[tn];

				f[tn]=g[x]+1;

				id[tn]=x;

			}

			else g[tn]=max(g[tn],g[x]+1);

		}

		dp(tn,x);

	}

}

inline int find(int x,int y)

{

	int l=0,r=G[x].size()-1;

	while(l+1<r)

	{

		int mid=(l+r)>>1;

		if(c[x][mid]<=y)l=mid;

		else r=mid;

	}

	if(c[x][r]<=y)return r;

	return l;

}

inline ll calc(int x,int y)

{

	if(H[x].find(y)!=H[x].end())return H[x][y];

	int cc=max(w[x],w[y]);

	ll ans=0;

	vep(0,G[x].size(),i)

	{

		if(c[y][0]>cc-c[x][i]-1)

		{

			ans+=(ll)(1+c[x][i])*G[y].size()+G[y][G[y].size()-1];

			continue;

		}

		if(c[y][c[y].size()-1]<=cc-c[x][i]-1)

		{

			ans+=(ll)G[y].size()*cc;

			continue;

		}

		int ww=find(y,cc-c[x][i]-1);

		ans+=(ll)(ww+1)*cc+G[y][G[y].size()-1]-G[y][ww]+(1+c[x][i])*(G[y].size()-ww-1);

	}

	H[x][y]=ans;return ans;

}

int main()

{

	//freopen("1.in","r",stdin);

	get(n);get(m);get(Q);

	rep(1,m,i)add(read(),read());

	rep(1,n,i)

	{

		if(vis[i])continue;

		mx=top=0;++cnt;dfs(i,0);dp(i,0);

		sort(s+1,s+1+top);w[cnt]=mx;

		rep(1,top,j)G[cnt].pb(s[j]),c[cnt].pb(s[j]);

		rep(1,top-1,j)G[cnt][j]+=G[cnt][j-1];

	}

	rep(1,Q,i)

	{

		int get(x),get(y);

		if(vis[x]==vis[y]){puts("-1");continue;}

		x=vis[x];y=vis[y];

		if(G[x].size()>G[y].size())swap(x,y);

		if(G[x].size()==G[y].size()&&x>y)swap(x,y);

		printf("%.7lf\n",1.0*calc(x,y)/(G[x].size()*G[y].size()));

	}

	return 0;

}