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

#define int long long
typedef pair<int, int> pii;

int a, b;
double c;

int32_t main() {
    cin.tie(0) -> sync_with_stdio(false);
    cin >> a >> b >> c;
    cout << (int) (a + b) * (c + 1 + 1e-6) << endl;
    return 0;
}