#include<cstdio>
#define rep(i,a) for(int i=0;i<(a);++i)

int main()
{
	int N, ans = 0;
	scanf( "%d", &N );
	rep( i, N )
	{
		int H, M, h, m;
		scanf( "%d:%d %d:%d", &H, &M, &h, &m );
		if( H*60+M > h*60+m )
			h += 24;
		ans += h*60+m-H*60-M;
	}

	printf( "%d\n", ans );

	return 0;
}