#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

void solve(){
    ll n;
    cin>>n;
    vector<ll> s;
    for(ll i=1;i<=n;i++){
        ll x,y;
        char ch;
        cin>>x>>ch>>y;
        s.push_back(x*60+y);
    }
    sort(s.begin(),s.end());
    ll ans=2;
    ll lstt=0,llstt=-100;
    for(ll i=0;i<s.size();i++){
        if(s[i]-llstt<=10) ans=min(ans,0ll);
        if(s[i]-lstt<=10) ans=min(ans,1ll);
        llstt=lstt;
        lstt=s[i];
    }
    cout<<ans<<'\n';
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    int n=1;
   // cin>>n;
    while(n--)solve();
    return 0;
}