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


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