#include <bits/stdc++.h>

using namespace std;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
}

int main() {
    fast_io();
    int w, z;
    double b;
    cin >> w >> z >> b;
    cout << (int)round(w * (b + 1) + z * (b + 1)) << endl;
}