N = int(input())
X = list(map(int,input().split()))
X = sorted(X)
D = []
counter = 0
for i in range(N-1) :
    if X[i+1] - X[i] != 0 :
        d = X[i+1] - X[i]
        D.append(d)

if len(D) != 0 :
    checker = D[0]
    if N-1 == D.count(checker) :
        print("YES")
    else :
        print("NO")
else :
    print("NO")