N = int(input())
L = sorted(list(map(int, input().split())))

d = L[1] - L[0]
if d == 0:
    print("NO")
    exit()

for i in range(2, N):
    print(L[i] - L[i - 1])
    if L[i] - L[i - 1] == d:
        print("NO")
        exit()

print("YES")