#include <bits/stdc++.h>
#define REP(i,n) for(int i = 0; i < (int)(n); ++i)
using namespace std;

int main() {
    int N;
    cin >> N;
    int H, M, h, m;
    char c;
    int ans = 0;
    REP(i,N){
        cin >> H >> c >> M >> h >> c >> m;
        ans += ( (h*60+m)>(H*60+M) ? (h*60+m)-(H*60+M) : 1440-(H*60+M)+(h*60+m) );
    }
    cout << ans << endl;
    return 0;
}