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

int main() {

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