#include<bits/stdc++.h>
using namespace std;
#define int            int64_t
#define double         long double
#define nitro          ios_base::sync_with_stdio(false);cin.tie(0);
#define vi             vector<int64_t>
#define pub            push_back
#define puf            push_front
#define pob            pop_back
#define pof            pop_front
#define PI             3.1415926535897932384626433832795
#define read(a)        for(auto& x : a) cin>> x
#define endl           '\n'
#define gap            ' '
#define min3(a,b,c)    min(a, min(b, c))
#define max3(a,b,c)    max(a, max(b, c))
#define MOD            1000000007
//freopen("input.txt","r",stdin);
//freopen("output.txt","w",stdout);
int32_t main()
{
    nitro
    int n;cin>>n;
    int a=ceil(sqrt(n));
    for(int i=a;~i;--i)
    if(i*i<=n) return cout<<i*i,0;
}
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll INF=1LL<<60;
const int inf=1<<30;
const int mod=1e9+7;
const int MOD=998244353;
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;cin >> n;
    cout << n/3 << endl;
}