#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define Would
#define you
#define please


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int N;
	cin >> N;

	int H = 0;
	int M = 0;
	rep(i, N) {
		string S, T;
		cin >> S >> T;
		int A = S.find(':');
		int B = T.find(':');

		int H1, H2, M1, M2;
		H1 = stoi(S.substr(0, A));
		H2 = stoi(T.substr(0, B));
		M1 = stoi(S.substr(A + 1, S.size() - A - 1));
		M2 = stoi(T.substr(B + 1, T.size() - B - 1));
		if (H1 * 60 + M1 > H2 * 60 + M2) H2 += 24;
		H += H2 - H1;
		M += M2 - M1;
	}
	co(H * 60 + M);

	Would you please return 0;
}