#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

int main(){
    int n, h1, m1, h2, m2, b, a, sum1;
    char c;
    cin >> n;
    for (int i = 0; i < n; i++){
        cin >> h1 >> c >> m1 >> h2 >> c >> m2;
        if (h1 > h2 || (h1 == h2 && m1 > m2)) h2 += 24;
        b = h1*60+m1;
        a = h2*60+m2;
        sum1 += (a - b);
    }
    cout << sum1 << endl;
}