//By SiriusRen

#include <bits/stdc++.h>

const int N=;

int n,m,vis[N],now=;

double p,r[N],tree[N*],ans;

struct Node{int x,y;}node[N];

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

void insert(int l,int r,int pos,int num,double wei){

    if(l==r){tree[pos]+=wei;return;}

    int mid=(l+r)>>,lson=pos<<,rson=pos<<|;

    if(mid<num)insert(mid+,r,rson,num,wei);

    else insert(l,mid,lson,num,wei);

    tree[pos]=tree[lson]+tree[rson];

}

double query(int l,int r,int pos,int L,int R){

    if(L>R)return ;

    if(l>=L&&r<=R)return tree[pos];

    int mid=(l+r)>>,lson=pos<<,rson=pos<<|;

    if(mid<L)return query(mid+,r,rson,L,R);

    else if(mid>=R)return query(l,mid,lson,L,R);

    else return query(l,mid,lson,L,R)+query(mid+,r,rson,L,R);

}

double w(int now,int t){return p*r[t-]/(-r[vis[node[now].x]]);}

int main(){

    scanf("%d%d%lf",&n,&m,&p),r[]=;

    for(int i=;i<=;i++)r[i]=r[i-]*(-p);

    for(int i=;i<=m;i++)scanf("%d%d",&node[i].x,&node[i].y),vis[node[i].x]++;

    std::sort(node+,node++m,cmp);

    for(int i=,t=;i<=n;i++,t=)while(node[now].x==i)

        t++,insert(,n,,node[now].y,w(now,t)),

        ans+=w(now,t)*query(,n,,node[now].y+,n),now++;

    printf("%.2f\n",ans);

}