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

int comp(const void *arg1, const void *arg2) {
	return *(int *)arg1 - *(int *)arg2;
}

int main(){
  int n, i, ans = 1;
  scanf("%d", &n);
  int duck[n];

  for(i = 0; i < n; i++){
    scanf("%d", &duck[i]);
  }

  qsort(duck, n, sizeof(int),comp);

  int a = duck[1] - duck[0];

  for(i = 2; i < n; i++){
    if((duck[i] - duck[i-1]) != a || duck[i] == duck[i-1]){
      ans = 0;
      break;
    }
  }

  if(ans == 1){
    printf("YES\n");
  }else{
    printf("NO\n");
  }

  return 0;
}