#include <stdio.h>

int main(){
  int w, h;
  long int n, k;
  long int end;

  scanf("%d%d%ld%ld", &h,&w,&n,&k);
  end = w * h;

  if((end % (n+1)) == k || end){
    printf("YES\n");
  }else{
    printf("NO\n");
  }
  return 0;
}