#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,ans;
    cin>>n;
    vector<vector<int>> a(n),b(n);
    for(int i=0;i<n;++i){
        string s,t,tmp;
        cin>>s>>t;
        istringstream ss(s),st(t);
        while(getline(ss,tmp,':')){
            a[i].emplace_back(stoi(tmp));
        }
        while(getline(st,tmp,':')){
            b[i].emplace_back(stoi(tmp));
        }
    }
    for(int i=0;i<n;++i){
        int ta=60*a[i].front()+a[i].back(),tb=60*b[i].front()+b[i].back();
        if(ta>tb)tb+=60*24;
        ans+=tb-ta;
    }
    cout<<ans<<endl;
}