#include <iostream>
using namespace std;

int main(){
    int N;
    cin >> N;
    
    int res = 0;
    for(int i=0;i<N;i++){
        int h1, m1, h2, m2;
        scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
        
        int start = h1 * 60 + m1;
        int end = h2 * 60 + m2;
        
        int tm = end - start;
        if(tm < 0)tm += 24 * 60;
        
        res += tm;
    }
    
    cout << res << endl;
    return 0;
}