#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <list>
#include <map>
#include <queue>
#include <iterator>
#include <cmath>
#include <iomanip>
using namespace std;

using ull = unsigned long long;
using ll = long long;

pair<int,int> getHS(string data)
{
    pair<int,int>  rtn;
    for(int i =0; i < data.size(); ++i)
    {
        if(data.at(i) == ':')
        {
            rtn.first = stoi(data.substr(0,i));
            rtn.second = stoi(data.substr(i+1));
            break;
        }
    }

    return rtn;
}

int main()
{
    int n;
    cin >> n;
    vector<string> a(n);
    vector<string> b(n);

    for(int i =0; i < n; ++i)
    {
        cin >> a.at(i);
        cin >> b.at(i);
    }

    int sum = 0;
    for(int i =0; i < n; ++i)
    {
        pair<int,int> first;
        pair<int,int> second;
        first = getHS(a.at(i));
        second = getHS(b.at(i));

        sum += (60-first.second + second.second);

        int sub = second.first - first.first - 1;
        if(sub >= -1)
        {
            sum += sub * 60;
        }
        else
        {
            sum += (24 + sub) * 60;
        }
    }

    cout << sum << endl;
}