#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int f(int x)
{
int res=x;
while(x>=3)
{
int m=x/3;
res+=m;
x%=3;
x+=m;
}
return res;
}
int main()
{
int n;
cin>>n;
int l=0,r=n,mid;
while(l<=r)
{
mid=(l+r)/2;
if(f(mid)<n)
{
l=mid+1;
}
else if(f(mid)>n)
{
r=mid-1;
}
else
{
break;
}
}
cout<<mid;
return 0;
}
就一个数据点错了