n = int(input())
X = sorted(list(set(map(int,input().split()))))
if n != len(X):
    print("NO")
else:
    cnt = X[1] - X[0]
    for i in range(1,n-1):
        if cnt != X[i+1] - X[i]:
            print("NO")
            exit()
    print("YES")