#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    int n;
    cin >> n;

    int ret = 0;
    for(int i=0; i<n; ++i){
        int h1, m1, h2, m2;
        char c;
        cin >> h1 >> c >> m1 >> h2 >> c >> m2;

        m1 += h1 * 60;
        m2 += h2 * 60;
        ret += (m2 - m1 + 24 * 60) % (24 * 60);
    }
    cout << ret << endl;

    return 0;
}