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


int main() {
    
    int a,b;
    long int n;
    cin>>a>>b>>n;
    
    int x = 0.5 * n * (a + b);
    
    int STDOUT = x % 7;
    cout<<STDOUT;
    return 0;
}