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

int comp(const void* a, const void* b) {
  return *(int*)a - *(int*)b;
}
int main(void) {
  int n, d, a, i, s[1000000];
  scanf("%d", &n);

  for( i = 0; i < n; i++ )
  scanf("%d", &s[i]);
  qsort(s, n, sizeof(int), comp);
  d = s[1] - s[0];

  for( i = 1; i < n - 1; i++ ) {
    a = s[i+1] - s[i];
    if( a == 0 || d != a) {
      printf("NO\n");
      return 0;
    }
    d = a;
  }
  printf("YES\n");
  return 0;
}