c289

/* c289            */
/* AC (8ms, 664KB) */
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

vector<string> v(10000);
int n, similar = 0;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    while(cin >> n && n)
    {
        similar = 0;
        for(int i = 0; i < n && cin >> v[i]; i++);
        sort(v.begin(), v.begin() + n);
        for(int i = 0; i < n - 1; i++)
        {
            int tmp = 0, length = min(v[i].length(),v[i + 1].length());
            for(int j = 0; j < length; j++)
                if(v[i][j] == v[i+1][j]) tmp++;
                else break;
            similar = (tmp > similar ? tmp : similar);
        }
        cout << similar << '\n';
    }
    return 0;
}