#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;
    long int v,r;
    scanf("%d %d %d",&a,&b,&t);
    v=1000000000+7;
    r=(0.5*a*t)+(0.5*b*t);
    r=r%v;
    printf("%ld",r);
    return 0;
}