#!/usr/bin/env python3


def main():
    _ = int(input())
    xs = sorted(int(x) for x in input().split())
    ds = [xj - xi for xi, xj in zip(xs[:-1], xs[1:])]
    print("YES" if ds[0] > 0 and all(d == ds[0] for d in ds) else "NO")


if __name__ == "__main__":
    main()