#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;

int n;
vector<int> tme;

void solve() {
    cin >> n;
    tme.resize(n);
    for (int i = 0; i < n; ++i) {
        string s;
        cin >> s;
        tme[i] += (s[0] - '0') * 60;
        tme[i] += (s[2] - '0') * 10;
        tme[i] += (s[3] - '0') * 1;
    }
    int mi2 = 1e9;
    for (int i = 0; i+2 < n; ++i) {
        int d = tme[i+2] - tme[i];
        mi2 = min(mi2, d);
    }
    int mi = 1e9;
    for (int i = 0; i+1 < n; ++i) {
        int d = tme[i+1] - tme[i];
        mi = min(mi, d);
    }
    dbg(mi);
    if (mi2 <= 10) {
        cout << 0 << '\n';
    }
    else if (mi <= 10) {
        cout << 1 << '\n';
    }
    else {
        cout << 2 << '\n';
    }
}

int main() {
    solve();
}