#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int (i) = 0 ; (i) < (int)(n) ; (i)++)
#define REP(i,a,b) for(int (i) = a ; (int)(i) <= (int)(b) ; (i)++)
#define all(n) (n).begin(),(n).end()
typedef long long ll;
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<long long,long long> Pii;
typedef vector<Pii> VPii;

int f(string s){
	s[s.find(":")] = ' ';
	stringstream ss(s);
	int h,m;
	ss >> h >> m;
	return h * 60 + m;
}

int main(){
	int n;
	cin >> n;
	int sum = 0;
	rep(i,n){
		string a,b;
		cin >> a >> b;
		int A = f(a);
		int B = f(b);
		if( A > B ) B += 24 * 60;
		sum += B - A;
	}
	cout << sum << endl;
}