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

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

int main() {
int h,m ,H,M;
char tmp;
int n,sum=0;
cin>>n;
for (int i = 0; i < n; ++i) {
	cin>>h>>tmp>>m>>H>>tmp>>M;
	int tt=h*60+m;
	int ttt=H*60+M;
	sum+=tt<ttt?ttt-tt:1440+ttt-tt;
}
cout<<sum<<endl ;

}