#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {

    int a;
    int b,c,d,e,n;
    
    n=(pow(10,9)+7);
    scanf("%d%d%d",&a,&b,&c);
    d=((0.5*a*c)+(0.5*b*c));
    e=d%n;
    
    printf("%d",e);/* Enter your code here. Read input from STDIN. Print output to STDOUT */    
    return 0;
}