题意：



思路：

贪心 能不覆盖的就不盖

写得很乱 左闭右开的 temp

//By SiriusRen

#include <queue>

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;

int n,l,temp,ans;

struct Node{int from,to;}node[10050];

priority_queue<Node>pq;

bool operator < (Node a,Node b){

    return a.from>b.from;

}

int main(){

    scanf("%d%d",&n,&l);

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

        scanf("%d%d",&node[i].from,&node[i].to),node[i].to--;

        pq.push(node[i]);

    }

    while(!pq.empty()){

        Node t=pq.top();pq.pop();

        if(temp<=t.from){

            int rec=(t.to-t.from+1)/l;

            ans+=rec;

            temp=t.from+l*rec;

            if(temp<=t.to)ans++,temp+=l;

        }

        else if(temp>t.to)

        {

            continue;

        }

        else{

            int rec=(t.to-temp+1)/l;

            ans+=rec;temp+=l*rec;

            if(temp<=t.to)ans++,temp+=l;

        }

    }

    printf("%d\n",ans);

}