#include <iostream>
#include <list>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdint.h>
using namespace std;

using uint = unsigned int;
using ll = long long;

#define CIN( LL , A ) LL A; cin >> A 

void SetTime( const string& HM , ll& time );

int main()
{

  CIN( ll , N );
  string HM;
  string hm;
  ll answer = 0;
  ll time;

  for( uint i = 0 ; i < N ; i++ ){

    cin >> HM;
    cin >> hm;
    SetTime( hm , time );
    ll d = time;
    SetTime( HM , time );
    d -= time;

    if( d < 0 ){

      d += 1440;
      
    }

    answer += d;
    
  }

  cout << answer << endl;
  return 0;

}

void SetTime( const string& HM , ll& time )
{

  const uint& size = HM.size();
  ll H = 0;
  ll M = 0;
  bool found = false;
  
  for( uint i = 0 ; i < size ; i++ ){

    const string s = HM.substr( i , 1 );
    
    if( s == ":" ){

      found = true;

    } else if( found ){

      M = 10 * M + stoi( s );

    } else {

      H = 10 * H + stoi( s );

    }

  }

  time = H * 60 + M;
  return;

}