N = int(input())
A = list(map(int, input().split()))
D = [0] * 50
for i in range(N):
  D[A[i]] += 1

ans = 0
for i in range(1, 50):
  if D[i] > 0 and D[i - 1] == 0:
    ans += D[i] * i

print(ans)