#include <iostream>
using namespace std;
int main()
{
    long long n,*a,*s,*z,*d,m;
    cin>>n;
    new long long ;a[n];
    new long long ;s[n];
    new long long ;z[n];
    new long long ;d[n];
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        s[i]=a[i];
        z[i]=s[i];
        a[i]=a[i]/10;
        z[i]=z[i]%10;
        s[i]=a[i];
        for(int j=1;j<=z[i];j++)
        {
            d[i]=a[i]*s[i];
        }
    }
    for(int i=0;i<n;i=i+2)
        m=d[i]+d[i+1];
    cout<<m;
    return 0;
}