```cpp
#include<bits/stdc++.h>
#define ll long long
#define N 2000001
using namespace std;
ll n=0;
ll ptime,l=0,flag[N],start[N],pend[N],count=0;
int main(){
cin>>ptime>>n;
for(int i=1;i<=n;i++){
cin>>start[i]>>pend[i];
}
for(int i=0;i<=ptime;i++){//ptime=500
for(int j=1;j<=n;j++){//n=3
if(start[j]==i){
//cout<<"find"<<start[j]<<endl;
for(int m=start[j];m<=pend[j];m++){
flag[m]++;
}
}
}
}
int res = 0;
for (int i = 0; i <= ptime; i++)
if(flag[i] == 0)
res++;
cout << res << endl;
return 0;
}
```
by Akomiju @ 2023-08-05 22:34:28
有//prime=500那行注释的for应该从0开始，因为起点是0不是1
最后的循环如果ptime--，那么for的结束条件也变了
by Akomiju @ 2023-08-05 22:35:19