#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstring>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

using namespace std;

int main()
{
	int n;
	cin >> n;

	int ans = 0;

	rep(i,n)
	{
		int H,M,h,m;
		char c;

		cin >> H >> c >> M >> h >> c >> m;

		int s = H*60 + M;
		int t = h*60 + m;
		int d[24*60];
		memset(d, 0, sizeof(d));

		if(H > h) {
			rep(j, t) {
				d[j]++;
			}

			REP(j, s, 24 * 60) {
				d[j]++;
			}
		} else {
			REP(j, s, t) {
				d[j]++;
			}
		}

		int cnt = 0;
		rep(j, 24*60) {
			if(d[j] > 0) cnt++;
		}

		ans += cnt;
	}

	cout << ans << endl;
	
	return 0;
}