#include <stdio.h>
#include <stdlib.h>
int cmp(const void *a, const void *b) {
  return *(int*)a - *(int*)b;
}
int main() {
  int N;
  int *X;
  int i;
  scanf("%d",&N);
  X = (int*)malloc(sizeof(int)*N);
  for (i=0; i<N; i++) {
    scanf("%d",X+i);
  }
  qsort(X, N, sizeof(int), cmp);
  int d = X[1] - X[0];
  int f = 0;
  if (d != 0) {
    for (i=2; i<N; i++) {
      if (d != (X[i]-X[i-1])) {
        f = 1;
        break;
      }
    }
  } else {
    f = 1;
  }
  if (f == 0) {
    printf("YES\n");
  } else {
    printf("NO\n");
  }
  return 0;
}