#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
using namespace std;
#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,P> Q;

const int inf = (int)1e9; 

ll gcd(ll a, ll b) {
	if (b > a) {
		ll tmp = b;
		b = a;
		a = tmp;
	}
	if (a%b == 0)return b;
	else return gcd(b, a%b);
}

int main(void){
	int n;
	cin>>n;
	int ans = 0;
	for(int i=0;i<n;i++){
		int h1,w1,h2,w2;
		char x1,x2;
		cin>>h1>>x1>>w1;
		cin>>h2>>x2>>w2;
		if(h1<h2){
			int tmp1 = h1*60+w1;
			int tmp2 = h2*60+w2;
			ans +=tmp2-tmp1;
		}
		else{
			int tmp1 = h1*60+w1;
			int tmp2 = (h2+24)*60+w2;
			ans +=tmp2-tmp1;
		}
	}
	cout<<ans<<endl;
	return 0;
}