#!/usr/bin/env python

from collections import Counter

def main():
    n = int(input().strip())
    xs = [int(x) for x in input().split()]
    xv = Counter(xs).values()
    if max(xv) > 1:
        print('NO')
        exit()
    xs.sort()
    dx = xs[1] - xs[0]
    for i in range(1,n):
        if xs[i] - xs[i-1] != dx:
            print('NO')
            exit()
    print('YES')

if __name__ == '__main__':
    main()