#include "bits/stdc++.h"

using namespace std;
using ll = long long;
const double pi = acos(-1);
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v) {
	REP(i, v.size()) { if (i)os << " "; os << v[i]; }return os;
}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v) {
	REP(i, v.size()) { if (i)os << endl; os << v[i]; }return os;
}

int main() {
	ll n, sh, sm, gh, gm;
	string s1, s2;
	ll ans = 0;

	cin >> n;

	REP(i, n) {
		cin >> s1 >> s2;
		if (s1[1] == ':') {
			sh = stoll(s1.substr(0, 1));
			sm = stoll(s1.substr(2));
		}
		else {
			sh = stoll(s1.substr(0, 2));
			sm = stoll(s1.substr(3));
		}
		if (s2[1] == ':') {
			gh = stoll(s2.substr(0, 1));
			gm = stoll(s2.substr(2));
		}
		else {
			gh = stoll(s2.substr(0, 2));
			gm = stoll(s2.substr(3));
		}
		if (sm > gm) {
			ans += (gm + 60 - sm) % 60;
			sh = (sh + 1) % 24;
		}
		else {
			ans += gm - sm;
		}
		if (sh > gh) {
			ans += (gh + 24 - sh) % 24 * 60;
		}
		else {
			ans += (gh - sh) * 60;
		}
	}

	cout << ans << endl;
}