#include<stdio.h>
#include<stdbool.h>
#include<string.h>
#include<stdlib.h>
int main(void)
{
  int w;   scanf("%d",&w);
  int z;   scanf("%d",&z);
  double b;scanf("%lf",&b);
  printf("%d", (int)((b+1.0f)*(w+z)));
  return 0;
}