#include<iostream>

#include<cstdio>

#include<cmath>

#include<cstdlib>

#include<cstring>

#include<algorithm>

#include<vector>

using namespace std;

int read()

{

    int x=,f=;char c=getchar();

    while (c<''||c>'') {if (c=='-') f=-;c=getchar();}

    while (c>=''&&c<='') x=(x<<)+(x<<)+(c^),c=getchar();

    return x*f;

}

#define N 500010

#define double long double

int n,m;

double p,tree[N],q[N],ans;

vector<int> a[N];

double query(int k){double s=;while (k) s+=tree[k],k-=k&-k;return s;}

void ins(int k,double s){while (k<=n) tree[k]+=s,k+=k&-k;}

int main()

{

#ifndef ONLINE_JUDGE

    freopen("bzoj4481.in","r",stdin);

    freopen("bzoj4481.out","w",stdout);

    const char LL[]="%I64d\n";

#else

    const char LL[]="%lld\n";

#endif

    n=read(),m=read();cin>>p;

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

    {

        int x=read(),y=read();

        a[x].push_back(y);

    }

    int cnt=;

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

    {

        sort(a[i].begin(),a[i].end());

        int s=a[i].size();

        double v=;

        for (int j=;j<s;j++) q[j]=v*p,v*=-p;

        for (int j=;j<s;j++) q[j]/=-v;

        for (int j=;j<s;j++) ans+=q[j]*(cnt-query(a[i][j]));

        for (int j=;j<s;j++) ins(a[i][j],q[j]);

        cnt+=s>;

    }

#undef double

    double p=ans;printf("%.2f",p);

    return ;

}