求Hack，马蜂良好

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define div() cout << "\n-----------------------\n";
#define debug(n) cout << #n << " = " << n << "\n";
#define deb(n) cout << #n << " = " << n << "    ";
int n;int vis[100005];int cnt;
int a[100005],b[100005];int cnt1,cnt2;
signed main(){
	cin >> n;
	for(int i = 1;i <= n;i++){
		int x;cin >> x;
		vis[x] = 1;
	}
	for(int i = 1;i < n*2;i++){
		if(vis[i] == 1){
			if(vis[i+1]==0){vis[i] = -2;vis[i+1] = -1;cnt++;}
		}
	}
	for(int i = 1;i <= n*2;i++){
		if(vis[i] == 0)b[++cnt2] = i;
		else if(vis[i] == 1)a[++cnt1] = i;
	}
	int i = 1,j = 1;
	while(i <= cnt1 && j <= cnt2){
		if(b[j] > a[i]){
			cnt++;j++;i++;
		}
		else j++;
	}
	cout << cnt;
	return 0;
}