var90_2009_s2_5

#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int a[25][25];
int main ()
{
    int  i,j,n,c1=0,c2=0;
    float s1=0,s2=0,m1,m2,rez;
    cin>>n;
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=n;j++)
        {
            cin>>a[i][j];
        }
    }
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=n;j++)
        {
            if (i<j)
            {
                if (a[i][j]>0)
                {
                    s1=s1+a[i][j];
                    c1++;
                }
            }
            else if (i>j)
            {
                if (a[i][j]>0)
                {
                    s2=s2+a[i][j];
                    c2++;
                }
            }
        }
    }
    m1=1.00*s1/c1;
    m2=1.00*s2/c2;
    cout<<setprecision(2)<<fixed<<floor((m1-m2)*100)/100;
    return 0;
}
/*
-1 2 -4 5
0 6 3 1
2 4 2 0
3 -5 1 -3
*/