# -*- coding: utf-8 -*-
"""
No.406 鴨等間隔の法則
https://yukicoder.me/problems/no/406

"""
import sys
from sys import stdin

input = stdin.readline


def solve(positions):
    result = 'YES'
    positions.sort()
    dist = positions[1] - positions[0]
    if dist == 0:
        return 'NO'

    for a, b in zip(positions, positions[1:]):
        if b - a != dist:
            result = 'NO'
            break
    return result


def main(args):
    N = int(input())
    positions = [int(x) for x in input().split()]
    ans = solve(positions)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])