#include <iostream>
using namespace std;

int main(){
   int ans = 0,n;
   char colon;
   cin >> n;
   for(int i = n,H,M,h,m;i--;){
      cin >> H >> colon >> M >> h >> colon >> m;
      while(H != h || M != m){
         ans++;
         if(++M == 60){
            M = 0;
            if(++H == 24) H = 0;
         }
      }
   }
   cout << ans << endl;
}