pion1

#include <iostream>
using namespace std;
int n,i,j,a[101][101],c[101][101];

void citire()
{ int i,j;
  cin>>n;
  for(i=1;i<=n;++i)
	for(j=1;j<=n;++j)
        cin>>a[i][j];
}

void pd()
{
    int i,j;
    for(i=2;i<=n;++i)
        for(j=1;j<=n;++j)
            if(a[i][j]==0)
                c[i][j]=c[i-1][j];
            else
                if(c[i-1][j-1]>c[i-1][j+1])
                    c[i][j]=c[i-1][j-1]+1;
                else
                    c[i][j]=c[i-1][j+1]+1;
}

void afis()
{
    int MAX=0;
    for(j=1;j<=n;j++)
        if(c[n][j]>MAX)
            MAX=c[n][j];
    cout<<MAX;
}

int  main()
{
    citire();
    pd();
    afis();
    return 0;
}