#include<iostream>
#include<string>
#include<cstring>
#include<complex>
#include<vector>
#include<algorithm>
#include<cstdlib>
#include<cmath>
#include<iomanip>
using namespace std;

#define REP(i, j) for (int i = 0; i < (int)j; ++i)
#define FOR(i, j, k) for (int i = (int)j; i < (int)k; ++i)
#define SORT(v) sort(v.begin(), v.end())
#define REVERSE(v) reverse(v.begin(), v.end())
typedef complex<double> P;
typedef vector<int> VI;
typedef long long LL;
typedef pair<int,int> PII;

int main() {

	int n;
	cin >> n;
	int d = 0;
	REP(i,n) {
		int hs, ms, hf, mf;
		scanf("%d:%d %d:%d", &hs, &ms, &hf, &mf);

		int s = hs * 60 + ms;
		int f = hf * 60 + mf;
		if (s < f) d += f - s;
		else d += (24 * 60 - s) + f;
	}

	cout << d << endl;

	return 0;
}