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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    unsigned long long N = 0;
    unsigned t, A, B;
    cin >> A >> B >> t;
    
    for (unsigned T = 1; T <= t; ++T) {
        N += 0.5 * A + 0.5 * B;
    }
    cout << N % 1000000007 << endl;
    return 0;
}