按左端点排序，贪心的选即可

#include<iostream>

#include<cstdio>

#include<algorithm>

using namespace std;

const int N=10005;

int n,l,p,ans;

struct qwe

{

	int x,y;

}a[N];

bool cmp(const qwe &a,const qwe &b)

{

	return a.x<b.x;

}

int read()

{

	int r=0,f=1;

	char p=getchar();

	while(p>'9'||p<'0')

	{

		if(p=='-')

			f=-1;

		p=getchar();

	}

	while(p>='0'&&p<='9')

	{

		r=r*10+p-48;

		p=getchar();

	}

	return r*f;

}

int main()

{

	n=read(),l=read();

	for(int i=1;i<=n;i++)

	   a[i].x=read(),a[i].y=read();

    sort(a+1,a+n+1,cmp);

    for(int i=1;i<=n;i++)

    	if(p<a[i].y)

		{

			p=max(p,a[i].x);

			while(p<a[i].y)

				ans++,p+=l;

		}

    printf("%d",ans);

	return 0;

}