#include <stdio.h>

int main () {
  int b0 = 0;
  int c0 = 0;
  int b1 = 0;
  int c1 = 0;
  
  int res = 0;
  
  int ans = 0;
  
  res = scanf("%d", &b0);
  res = scanf("%d", &c0);
  res = scanf("%d", &b1);
  res = scanf("%d", &c1);
  
  if (c0 < 0) {
    c0 += (1+(-c0)/b0)*b0;
  }
  if (c1 < 0) {
    c1 += (1+(-c1)/b1)*b1;
  }
  
  while (ans < b0*b1) {
    if (ans%b0 == c0%b0 && ans%b1 == c1%b1) {
      printf("%d\n", ans);
      return 0;
    }
    ans++;
  }
  
  printf("NaN\n");
  return 0;
}