#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#define m 1000000007

int main() {

    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    int a,b,g;
    long long int t;
    scanf("%d%d%lld",&a,&b,&t);
    long long int v=(0.5*a*t+0.5*b*t);
    g=v%m;
    printf("%d",g);
    return 0;
}