import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	// xor の性質 (X ^ Y) ^ X = Y より, F0, F1, F0 ^ F1, F0, F1, ... とループする.
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		
		long sum = 0;
		for(int i = 0; i < N; i++){
			final String[] ins = sc.next().split(":");
			final String[] outs = sc.next().split(":");
			
			final int H = Integer.parseInt(ins[0]);
			final int M = Integer.parseInt(ins[1]);
			final int h = Integer.parseInt(outs[0]);
			final int m = Integer.parseInt(outs[1]);
			
			sum += ((h - H + (h < H ? 24 : 0)) * 60 + (m - M));
		}
		
		System.out.println(sum);
	}
	
}