#include<bits/stdc++.h>
using namespace std;
long long carries;
const int MAXN=100010;
int a[MAXN],b[MAXN];
int main(void)
{
int n;
while(~scanf("%d",&n))
{
carries=0;
for(int i = 0; i < n; ++i)
{
scanf("%d",&a[i]);
}
int tmp=1;
for(int i = 1; i <= 9; ++i)
{
tmp*=10;
for(int j = 0; j < n; ++j)
{
b[j] = a[j]%tmp;
}
sort(b,b+n);
int left=n;
for(int j = 0; j < n; ++j)
{
while(left && b[j]+b[left-1]>=tmp)
--left;
if(left<=j)
carries+=(n-left-1); //去掉b[j]
else
carries+=(n-left);
}
}
carries/=2;
printf("%lld\n",carries);
}
return 0;
}
