#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin() , v.end()
#define REP(i, x, n) for(int i = x; i < n; i++)


int main(){
    int n; cin >> n;
    int H,M,h,m,sum=0;
    rep(i, n){
        scanf("%d:%d %d:%d", &H,&M,&h,&m);
        if(H > h || (H == h && M > m)) h+=24;
        sum += (h - H) * 60 + (m - M);
    }
    cout << sum << endl;
}