#include<bits/stdc++.h>
#define ll long long
#define N 2000001
ll n=0;
using namespace std;

int main(){
	ll time,l=0,flag[N],start[N],end[N],count=0;
	cin>>time>>n;
	for(int i=1;i<=n;i++){
		cin>>start[i]>>end[i];
	}
	for(int i=1;i<=time;i++){
		for(int j=1;j<=n;j++){
			if(start[j]==i){
				for(int m=start[j];m<=end[j];m++){
					flag[j]++;
				}
			}
		}
	}
	for(int i=1;i<=time;i++){
		if(flag[i]!=0){
			time--;
		}
	}
	cout<<time;
	return 0;
}

--------------------------------
Process exited after 1.23 seconds with return value 3221225725
Press any key to continue . . .

题目出自这里，要是有人能帮忙改一下就更好了P1047