#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,t,no_a=0,no_b=0;
    double no=0,p,mod,virus=0;
    cin>>a>>b>>t;
    no_a=(a*t)/2;
    no_b=(b*t)/2;
    no=(no_a+no_b);
    p=pow(10,9);
    mod=p+7;
    virus=fmod(no,mod);
    cout<<virus;
    return 0;
}