#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 */   
    
    const double abc = ( pow(10,9) + 7 );
    const float prob1 = 0.5;
    const float prob2 = 0.5;
    
    long double op;
    
    int a = 0, b = 0, t = 0;    
    cin >> a >> b >> t;
    
    long double tempans = 0;
    
    for(int i =1; i <= t; i++)
    {
        
    }
    
    op = (prob1 * a * t + prob2 * b * t);
    
    cout << fmod(op, abc);
    
    return 0;
}