import java.util.Scanner;

public class ISoar {
	Scanner in = new Scanner(System.in);
	
	void start() {
		while (true) {
			float L = in.nextFloat();
			if (L <= 0) return;
			while (true) {
				float x1 = in.nextFloat();
				float x2 = in.nextFloat();
				if (x1 > x2) break;
				L -= (x2 - x1);
			}
			System.out.printf("The total planting length is %.1f\n", L);
		}
	}
	
	public static void main(String[] args) {
		new ISoar().start();
	}
}