import java.util.Scanner;
import java.util.TreeSet;


public class PB {

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        float n = in.nextFloat();
        while(n>0){
            TreeSet<P> ps = new TreeSet<P>();
            float x = in.nextFloat();
            float y = in.nextFloat();
            while(x<=y){
                ps.add(new P(x,y));
                x = in.nextFloat();
                y = in.nextFloat();
            }
            
            float ans=n;
            float l=0, r=0;
            for(P p : ps){
                if(p.x>=r){
                    ans-=r-l;
                    l=p.x;
                    r=p.y;
                } else {
                    if(p.y>r)
                        r = p.y;
                }
            }
            ans-=r-l;
            System.out.printf("The total planting length is %.1f\n", ans);
            n = in.nextFloat();
        }
    }
    
    
    private static class P implements Comparable<P>{
        public float x;
        public float y;
        
        public P(float x, float y){
            this.x = x;
            this.y = y;
        }
        
        @Override
        public int compareTo (P arg0) {
            if(Math.abs(this.x-arg0.x)<1e-5){
                return (this.y-arg0.y)>0?1:-1;
            }
            return (this.x-arg0.x)>0?1:-1;
        }
        
    }
}