#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<LL,LL> PII;
const int N=4e5+10,M=2e6;
const int mod=998244353;
const LL P=1e9+7;
const LL INF=1e18;
LL h[N],e[M],ne[M],w[M],idx;
int T=1;





void solve(){
    int n;
    cin>>n;
    vector<int> a(n);

    for(auto &t:a){

        string s;
        cin>>s;


        int k=(s[0]-'0')*60+(s[2]-'0')*10+(s[3]-'0');

        t=k;
    }

    sort(a.begin(),a.end());


    int res=2;

    for(int i=1;i<n;i++) if(a[i]-a[i-1]<=10) res=1;
    for(int i=2;i<n;i++) if(a[i]-a[i-2]<=10) res=0;

    cout<<res<<endl;
}





 
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    //int T=1;

    //cin>>T;

    while(T--) solve();
 
    return 0;
}