#include<bits/stdc++.h>

using namespace std;
 
typedef long long int ll;
typedef long double ld;
#define f first
#define s second
#define pb push_back
#define pii pair<int, int>

 
const int N = 2e5 + 100;
const int inf = 1e9;
const ll mod =  998244353;




int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin >> n;
    vector<ll> a(n);
    for (int i = 0; i < n; i++) {
        ll x = 0;
        int k;
        for (int j = 0; j < 4; j++) {
            char c;
            cin >> k;
            x = (x << 8) + k;
            if (j < 3) cin >> c;
        }
        a[i] = x;
    }
    for (int b = 31; b >= 0; b--) {
        int same = 1;
        for (int i = 0; i < n; i++) {
            if ((a[i] >> b & 1) != (a[0] >> b & 1)) {
                same = 0;
                break;
            }
        }
        if (!same) {
            if (b == 31) cout << 32 << endl;
            else cout << 31 - b << endl;
            return 0;
        }
    }
    return 0;
}