#include <iostream>
#include <algorithm>

using namespace std;

const int N=30;

int n,t[N];
char s[N];

int main(){
	ios::sync_with_stdio(0),cin.tie(0);
	cin>>n;
	for (int i=1;i<=n;i++){
		cin>>s+1;
		t[i]=(s[1]-'0')*60+(s[3]-'0')*10+s[4]-'0'; 
	}
	sort(t+1,t+n+1);
	for (int i=1;i<=n-2;i++)
		if (t[i+2]-t[i]<10) cout<<"0",exit(0);
	for (int i=1;i<=n-1;i++)
		if (t[i+1]-t[i]<10) cout<<"1",exit(0);
	cout<<2; 
	return 0;
}