N = int(input())
List = list(map(int,input().split()))
List.sort()
Delta = []

for i in range(N-1):
    Delta.append(List[i+1]-List[i])
Delta_set = set(Delta)
if 0 in Delta_set:
    print("NO")
elif len(Delta_set) == 1:
    print("YES")
else:
    print("NO")