#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    int answer = 0;
    while(N--){
        string s; cin >> s;
        int one = 0,two = 0;
        for(auto c : s){
            if(c == ':') swap(one,two);
            else one *= 10,one += c-'0';
        }
        swap(one,two);
    
        int now = 0;
        now += (23-one)*60;
        now += 60-two;
        cin >> s; one = 0,two = 0;
        for(auto c : s){
            if(c == ':') swap(one,two);
            else one *= 10,one += c-'0';
        }
        swap(one,two);
        now += one*60+two;

        now %= 1440;
        answer += now;
    }
    cout << answer << endl;
}