#include<iostream>

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;
    
    int N,H,M,h,m;
    char c;
    
    cin >> N;
    int sumH=0, sumM=0;
    for(int i=0; i<N; i++) {
        cin >> H >> c >> M >> h >> c >> m;
     
        if (H>=h) {
            h += 23;
            m += 60;
        }
        
        sumH += h-H;
        //cout << h-H << endl;
        sumM += m-M;
        //cout << m-M << endl;
        if(H==h-23 && M>=m-60) { sumH-=24;} //日付を超えていたとき

    }
    
    cout << sumH*60 + sumM << endl;
    
    return 0;
}