C :

#include<stdio.h>
#include<string.h>
int main()
{
    int l,m,a[10006],x,y;
    while(scanf("%d%d",&l,&m)!=EOF)
    {
        for(int i = 0 ; i <= l ; i++)
            a[i]=1;
        while(m--)
        {
            scanf("%d%d",&x,&y);
            for(int i = x ; i <= y ; i++)
                if(a[i]==1)
                    a[i]=0;
        }
        int sum = 0 ;
        for(int i = 0 ; i <= l ; i++)
            if(a[i]==1)
            sum++;
        printf("%d\n",sum);
    }
    return 0;
}

C++ :

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;

int main()
{
    int l,m;
    cin>>l>>m;
    int i,a[10001];
    for(i=0;i<=l;i++)
        a[i]=1;
    while(m--)
    {
        int p,q;
        cin>>p>>q;
        for(i=p;i<=q;i++)
            a[i]=0;
    }
    int y=0;
    for(i=0;i<=l;i++)
        if(a[i])
           y++;
    cout<<y<<endl;
}

Pascal :

type
 rec=record
  x,y,l,r,c:longint;
 end;
var
 ans,l,m,i,x,y,tot:longint;
 tree:array[0..40000] of rec;
procedure make(l,r:longint);
var
 now:longint;
begin
 inc(tot);
 now:=tot;
 tree[now].x:=l;
 tree[now].y:=r;
 if l+1<=r then
 begin
  tree[now].l:=tot+1;
  make(l,(l+r) div 2);
  tree[now].r:=tot+1;
  make((l+r) div 2+1,r);
 end;
end;
procedure insert(v,x,y:longint);
begin
 if (x<=tree[v].x)and(tree[v].y<=y) then
 begin
  inc(tree[v].c);
  exit;
 end;
 if x<=(tree[v].x+tree[v].y) div 2 then insert(tree[v].l,x,y);
 if y>(tree[v].x+tree[v].y) div 2 then insert(tree[v].r,x,y);
end;
procedure find(v:longint);
begin
 if v=0 then exit;
 if tree[v].c>0 then
 begin
  inc(ans,tree[v].y-tree[v].x+1);
  exit;
 end;
 find(tree[v].l);
 find(tree[v].r);
end;
begin
 readln(l,m);
 make(1,l+1);
 for i:=1 to m do
 begin
  readln(x,y);
  insert(1,x+1,y+1);
 end;
 find(1);
 //writeln(ans,' ',l);
 writeln(l+1-ans);
end.

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		int L =sc.nextInt();
		int n=sc.nextInt();
		boolean[] flag = new boolean[L+1];
		for(int i=0;i<n;i++) {
			int x=sc.nextInt();
			int y=sc.nextInt();
			for(int j=x;j<=y;j++) {
				flag[j]=true;
			}
		}
		int num=L+1;
		for(int i=0;i<=L;i++) {
			if(flag[i]) {
				num--;
			}
		}
		System.out.println(num);
	}

}