N = int(input())
X = [int(i) for i in input().split()]
X = list(X)
X = sorted(X)
B = 0
for i in range(N-2):
    if X[1+i]-X[i] != X[1]-X[0]:
        B = 1
    if X[1+i]-X[i] == 0:
        B = 1
if B == 1:
    print("NO")
else:
    print("YES")