#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int n , m , p;
double f[1005][1005];
int main() {
    cin >> n >> m >> p ;
    for(int i = 1;i <= n;i++) f[i][m + 1] = 1e18;
    for(int i = 1;i <= m;i++) f[n + 1][i] = 1e18;
    for(int i = n;i >= 1;i--) {
        for(int j = m ; j >= 1;j--) {
            if(i == n && j == m) {
                f[i][j] = 0 ; continue ;
            }
            double a = f[i + 1][j] , b = f[i][j + 1];
            double del = max(a , b) - min(a , b);
            if(del >= p) {
                f[i][j] = 0.5 * min(a , b) + 0.5 * (min(a , b) + p / 2.0) ;
            }
            else {
                f[i][j] = 0.5 * min(a , b) + 0.5 * (min(a,b) + del / p * del / 2 + (1 - del / p) * del) ;
            }
            // printf("%d %d %lf\n",i,j,f[i][j]) ;
        }
    }
    printf("%.12lf\n",f[1][1]) ;
    return 0;
}