varianta90_II_5

#include <iostream>
using namespace std;
int a[21][21];
int main()
{
    int i,j,n,msus=0,nrsus=0,mjos=0,nrjos=0;
    cin>>n;
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n;j++)
        {
            cin>>a[i][j];
            if(i<j && a[i][j]>0)
            {
                msus+=a[i][j];
                nrsus++;
            }
            if(i>j && a[i][j]>0)
            {
                mjos+=a[i][j];
                nrjos++;
            }
        }
    }
    if(nrsus!=0 && nrjos!=0)
    {
        cout<<(double)msus/nrsus-(double)mjos/nrjos;
    }
    else
    {
        cout<<0;
    }
    return 0;
}