import java.util.*;

public class Yukicoder_70{
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int minute  = 0;
		for(int i=0;i<N;i++){
			String H = stdIn.next();
			String h = stdIn.next();
			int H_minp = 0;
			int h_minp = 0;
			int H_min = 0;
			int h_min = 0;
			int H_hour = 0;
			int h_hour = 0;
			for(int j=0;j<H.length();j++){
				if(':' == H.charAt(j)){
					H_minp = j;
					break;
				}
			}
			for(int j=0;j<h.length();j++){
				if(':' == h.charAt(j)){
					h_minp = j;
					break;
				}
			}

			for(int j=H_minp+1;j<H.length();j++){
				if(H.length() - j == 2){
					H_min += ((int)H.charAt(j)-(int)'0')*10;
				}
				else{
					H_min += ((int)H.charAt(j)-(int)'0');
				}
			}
			for(int j=h_minp+1;j<h.length();j++){
				if(h.length() - j == 2){
					h_min += ((int)h.charAt(j)-(int)'0')*10;
				}
				else{
					h_min += ((int)h.charAt(j)-(int)'0');
				}
			}
			minute += h_min - H_min;
			for(int j=0;j<H_minp;j++){
				if(H_minp-j==2){
					H_hour += ((int)H.charAt(j)-(int)'0')*10;
				}
				else{
					H_hour += ((int)H.charAt(j)-(int)'0');
				}
			}
			for(int j=0;j<h_minp;j++){
				if(h_minp-j==2){
					h_hour += ((int)h.charAt(j)-(int)'0')*10;
				}
				else{
					h_hour += ((int)h.charAt(j)-(int)'0');
				}
			}
			if(H_hour<=h_hour){
				minute += (h_hour-H_hour)*60;
			}
			else{
				minute += (24+h_hour-H_hour)*60;
			}
		}
		System.out.println(minute);
	}
}