#include<bits/stdc++.h>
using namespace std;
int n;
bool check(int x)
{
	int cnt=x;
	while(x>=3)
	{
		cnt+=x/3;
		x=x-(x/3*3+(x/3));
	}
	return cnt<n;
}
int main()
{
	cin>>n;
	int l=1,r=1e8,ans=-1;
	while(l<=r)
	{
		int mid=(l+r)/2;
		if(check(mid))
		{
			l=mid+1;
		}
		else
		{
			ans=mid;
			r=mid-1;
		}
	}
	cout<<ans
	return 0;
}

哪里错了？？？
最后祝大家国庆快乐