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


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