#include <bits/stdc++.h>
#define double long double
using namespace std;
const int N=1005;
int n,m;
double p;
double Calc[N][N];
double calc(int x,int y) {
    if(Calc[x][y])
        return Calc[x][y];
    if(x==1 && y==1) return 0;
    if(x==1)  return Calc[x][y]=p/4+calc(x,y-1);
    if(y==1) return Calc[x][y]=p/4+calc(x-1,y);
    double ret=0;
    double t1=calc(x-1,y),t2=calc(x,y-1);
    if(t1>t2) swap(t1,t2);
    ret+=t1;
    if(t2-t1<p) ret+=(p*t2-(t1-t2)*(t1-t2)/2)/p;
    else ret+=t1+p/2;

    return Calc[x][y]=ret/2;
}
signed main() {
    scanf("%d%d%Lf",&n,&m,&p);
    printf("%.10Lf",calc(n,m));
    return 0;
}