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

int main() {

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