#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
const ll MOD=1e9+7;
// head

const int N=25;
int a[N];

signed main() 
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

	int n;
	cin>>n;
	for (int i=1;i<=n;++i) {
		int h; cin>>h;
		char c; cin>>c;
		cin>>a[i];
		a[i]+=(h-7)*60;
	}
	sort(a+1,a+n+1);
	for (int i=1;i+2<=n;++i) {
		if (a[i+2]-a[i]<=10) {
			cout<<0;
			return 0;
		}
	}
	for (int i=1;i+1<=n;++i) {
		if (a[i+1]-a[i]<=10) {
			cout<<1;
			return 0;
		}
	}
	cout<<2; 
    return 0;
}