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


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int a, b, t;
    cin >> a >> b >> t;
    int modulo = (10^9) + 7;
    cout<< fmod((((a*0.5)+(b*0.5))*t),modulo);
    return 0;
}