#include <iostream>
#include <string>
#include <vector>
#include <sstream>

using namespace std;

vector<string> conv(string s) {
    istringstream iss(s); string tmp; vector<string> vec;
    while (getline(iss, tmp, ':')) vec.push_back(tmp);
    return vec;
}

int func(string s) {
    vector<string> vec;
    vec = conv(s);
    int a = 0, b = 0;
    a = stoi(vec.at(0));
    b = stoi(vec.at(1));
    return a * 60 + b;
}

int main() {
    int n;
    cin >> n;
    int a = 0, b = 0, ans = 0;
    string x, y;

    for (int i = 0; i < n; ++i) {
        cin >> x >> y;
        a = func(x);
        b = func(y);
        ans += ((1440 + b - a) % 1440);
    }
    cout << ans <<endl;
    return 0;
}