#include<bits/stdc++.h>
using namespace std;

const long long INF = 1LL << 60;
#define MOD 1000000007;

typedef long long ll;

#define writeln(n) cout<<n<<endl;
#define rep(i,n) for(int i=0; i<n; i++);

typedef pair<float, float> P;

typedef pair<string, int> Psi;


int main() {


	int n;
	cin>>n;

	int h,m,hh,mm;

	int sum=0;
	for(int i=0; i<n; i++){
		scanf("%d:%d",&h,&m);
		scanf("%d:%d",&hh,&mm);

		int hour=0;
		if(hh<h){
			hour += 24-h;
			hour +=hh;
		}else {
			hour += hh-h;
		}

		if(mm<m){
			sum += 60-m;
			sum +=mm;

			if(h ==0 && hh ==0){
			sum += 23*60;
			}else {
				sum += (hour-1)*60;
			}
		}else {
			sum += mm-m;
			sum += hour*60;
		}
	}

	writeln(sum);


}