#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    double n, m, p;
    cin >> n >> m >> p;
    cout << fixed << setprecision(15);
    if(n == 1 && m == 1){
        cout << p << '\n';
    }else if(n == 1 || m == 1){
        cout << 2 * p * p + (n * m - 2) * p * p * p << '\n';
    }else{
        cout << p * (4 * p * p + (2 * (n + m) - 8) * p * p * p + (n * m - 2 * (n + m) + 4) * p * p * p * p) << '\n';
    }
}