#include<bits/stdc++.h>
using namespace std;
typedef long long LL; 
LL check(LL x)
{
	LL res=0;
	LL t=x;
	while(x)
	{
		LL ge=x%10;
		res=res*10+ge;
		x/=10;
	}
	//cout<<res<<" "<<t<<endl;
	return res==t;
}
int main()
{
	LL n;
	cin>>n;
	LL ans=1;
	for(LL i=1;i*i*i<=n;i++) //枚举三次方 
	{
		if(check(i*i*i))
		{
			ans=i*i*i;
		//	cout<<ans<<endl;
		}
	}
	cout<<ans;
	return 0;
}