#F = [1, 1]
#for _ in range(10000):
#    F.append(F[-2]+F[-1])
#fs = set(F)

N, = map(int, input().split())
X = list(map(int, input().split()))
X.append(2*10**18)
X.append(2*10**18)
dp = [1] * (N+2)
R = 0

X.sort()
for i in range(N-1, -1, -1):
    if X[i+1] == X[i] + 2:
        dp[i] = dp[i+1] + 1
    if X[i+2] == X[i] + 2:
        dp[i] = dp[i+2] + 1
    if X[i+1] == X[i] + 1:
        R += dp[i+1]+1
    else:
        R += 1
#print(X)
#print(dp)
print(R)

#
#for i in range(2**N):
#    R = 0
#    Y = []
#    for j in range(i):
#        i, m = divmod(i, 2)
#        if m:
#            R += F[X[j]]
#            Y.append(X[j])
#    if R in fs:
#        print(R, Y)
#
#