C :

#include <stdio.h>
int main()
{int a[10001]={0},b,c,i,j,h=0;
scanf("%d%d",&b,&c);
while(c--)
{scanf("%d%d",&i,&j);
while(i<=j)
{
a[i++]=1;
};
};
while(b>=0)
{
if(a[b]==0)
h++;
b--;
};
printf("%d\n",h);
return 0;
}

C++ :

#include<iostream>
using namespace std;
int n,i,ans,all,r,l,j;
int c[1000001];
int main()
{
    cin>>all>>n;
    for(i=1;i<=n;i++)
    {cin>>l>>r;
    for(j=l;j<=r;j++)c[j]=1;
    }
    for(j=0;j<=all;j++)
    if(c[j]==0)ans++;
    cout<<ans;
    return 0;
}

Pascal :

var m,n,x,y,i,j,ans:longint;a:array[0..10000]of longint; 
begin
  readln(m,n); 
  for i:=1 to n do
    begin
      read(x,y); 
      for j:=x to y do a[j]:=1; 
    end; 
  for i:=0 to m do if a[i]=0 then ans:=ans+1; 
  writeln(ans); 
end.