#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 */ 
    float a,b,c;
    long long res,temp;
    cin>>a>>b>>c;
    temp=10+7;
    res=(0.5*a*c)+(0.5*b*c);
    cout<<res%temp;
    
    return 0;
}