#include <bits/stdc++.h>

#define pb push_back
#define pf push_front
#define mp make_pair
#define sz size
#define ll long long
#define ld long double
#define fs first
#define sc second
#define forn(i, f, t) for(int i = f; i < t; i++)
#define all(x) (x).begin(), (x).end()
#define ins insert

const int INF = 2147483647;
const int MOD = 1000000007;
const ll INF64 = 9223372036854775807;
const ld EPS = 1e-7;

using namespace std;

int check(const vector<int> &a, const vector<int> &b){
    int cur = 0;
    forn(i, 0, 6) cur += (a[i] == b[i]);
    return max(0, (6 - cur) / 2 + (6 - cur) % 2 - 1);
}


int main(){
    int n, t;
    scanf("%d", &n);
    vector<int> a[n];
    forn(i, 0, n){
        scanf("%d", &t);
        int k = 100000;
        while (k){
            a[i].pb(t / k);
            t %= k;
            k /= 10;
        }
    }
    int ans = 6;
    forn(i, 0, n) forn(j, i + 1, n) ans = min(ans, check(a[i], a[j]));
    printf("%d\n", ans);
    return 0;
}