#include<bits/stdc++.h>
using namespace std;
int n;
int main(){
  
	cin>>n;
	cout<<n*2;
	return 0;
}

太太太太简单了

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	cout<<a*2;
	return 0;
}

观察样例发现，答案就是 $n\times2$。（好神奇

#include<bits/stdc++.h>
#define int long long
#define INF 0x3f3f3f
using namespace std;
int n;
signed main(){
	cin>>n;
	cout<<n*2;
	return 0;
}