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

void HM( int &H, int &M, const char *S )
{
int iPos;

	if( S[ 1 ] == ':' )
	{
		iPos = 2;
		H = S[ 0 ] - '0';
	}
	else
	{
		iPos = 3;
		H = 10 * ( S[ 0 ] - '0' ) + S[ 1 ] - '0';
	}

	if( S[ iPos + 1 ] == '\0' )
		M = S[ iPos ] - '0';
	else
		M = 10 * ( S[ iPos ] - '0' ) + S[ iPos + 1 ] - '0';
}

int main()
{
int i;
int N;
int H;
int M;
int h;
int m;
int iSleep;
int iSum;
char S[ 100 ];
char T[ 100 ];

	cin >> N;

	iSum = 0;
	for( i = 0; i < N; i++ )
	{
		cin >> S;
		cin >> T;
		HM( H, M, S );
		HM( h, m, T );
		if( h > H || ( h == H && m >= M ) )
			iSleep = ( h - H ) * 60 + m - M;
		else
			iSleep = ( 24 + h - H ) * 60 + m - M;

		iSum += iSleep;
	}

	cout << iSum << endl;

	return 0;
}