#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int a, b, t;
    int ans = 0;
    int mod;
    cin >> a >> b >> t;
    ans = 0.5*a*t + 0.5*b*t;
    mod = pow(10,9)+7;
    ans = ans%mod;
    cout << ans;
    return 0;
}