#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,c,t,e;
    scanf("%d %d %d",&a,&b,&t);
     c=0.5*a*t+0.5*b*t; 
     e=c%1000000007;
    printf("%d",e);
    return 0;
}