import collections
import bisect
N = int(input())
A = list(map(int, input().split())) 
ans = 0
#a1
#a2=a1+k+10
#a3=a1+10
#a4=a1+k+10+1=a2+1
A13 = []
A24 = []
for i in range(N):
    for j in range(i+1,N):
        if A[i]==A[j]-10:
            A13.append([i,j])
        if A[i]==A[j]-1:
            A24.append([i,j])
ans = 0
for a1,a3 in A13:
    for a2,a4 in A24:
        if a1<a2<a3<a4 and A[a1]<A[a2]+10:
            ans+=1
print(ans)