#include <bits/stdc++.h>
using namespace std;
int tk(string s){
istringstream iss(s);
int k,q;
iss>>k;
iss.ignore();
iss>>q;
return k * 60 + q;
}
int main(){
int n;cin>>n;
int s =0;
for(int i=0;i<n;i++){
string d1,d2;
cin>>d1>>d2;
int d = tk(d2) - tk(d1);
d +=1440;
d%=1440;
s+=d;
}
cout<<s<<endl;
}