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

void sort(int *a, int size){
  int i, j, tmp;
  for(i = 0 ; i < size-1; i++){
    for(j = size-1; j > i; j--){
      if(a[j-1] > a[j]){
	tmp = a[j-1];
	a[j-1] = a[j];
	a[j] = tmp;
      }
    }
  }
}

int main(void){
  int i;
  int N, S[100000];
  int l, flag = 0;
  scanf("%d", &N);
  for(i = 0; i < N; i++){
    scanf("%d", &S[i]);
  }
  sort(S, N);
  l = abs(S[1] - S[0]);
  for(i = 1; i < N - 1; i++){
    if(l != abs(S[i+1] - S[i])){
      flag = 1;
      break;
    }
  }
  if(l != 0 && flag == 0) printf("YES\n");
  else printf("NO\n");
  return 0;
}