#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<string>
#include<vector>
#include<queue>
#include<utility>
#include<set>
#include<map>
#include<cctype>
#include<cmath>
#include<algorithm>
using namespace std;

#define RALL(x) (x).rbegin(),(x).rend()
#define ALL(x) (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define rev(j,m) for(int j=1;j<=(m);j++)
#define repp(k,l,r) for(int k=0;k<(l);k+=r)
#define EACH(itr,c) for(__typeof((c).begin()) itr=(c).begin(); itr!=(c).end(); itr++)
#define pb push_back


typedef long long ll;
typedef pair<int,int> P;
typedef vector<pair<int,int> > pii;
typedef map<string,int> mi;



int main(){
	int n,H,M,h,m,ans=0;
	char c;
	cin >> n;
	rep(i,n){
		int sum,sum2;
		scanf("%d:%d %d:%d",&H,&M,&h,&m);
		sum=H*60+M;
		sum2=h*60+m;
		sum2-=sum;
		if(sum2<0)sum2+=24*60;
		ans+=sum2;
	}
	printf("%d\n",ans);
	return 0;
}