N = int(input())

A = list(map(lambda x: [int(x), 1], input().split()))

ans = N

A.sort()

for i in range(N - 1):
    
    if A[i][0] == A[i + 1][0] - 1:
        
        ans += A[i][1]
        
        if i < N - 2 and A[i + 2][0] == A[i][0] + 2:
            
            A[i + 2][1] += A[i][1]
            
print(ans)