#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 */   
   int a,b,c;
    cin>>a>>b>>c;
    long int mod = 10000000007;
    int out,ans;
    out = (0.5*a*c) + (0.5*b*c);
    ans = out % mod;
    cout<<ans;
    
    return 0;
}