N = int(input())
L = list(map(int,input().split()))
L = sorted(L)
d = L[1] - L[0]
if d == 0 :
    ans = "NO"
else :
    for i in range(1,N-1) :
        if d != (L[i+1] - L[i]) :
            ans = "NO"
            break
    else :
        ans = "YES"
print(ans)