#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 */   
    int a,b;
    long int t ;
    cin>>a>>b>>t ;
    long int time ;
    time = (0.5*a)*t + (0.5*b)*t ;
    time = time%(10^9+7) ;
    cout<<time ;
    
    return 0;
}