#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define ps push
#define in insert
#define f first
#define s second
#define nl cout<<"\n"
#define ca(v) for(auto i:v) cout<<i<<" ";
#define cbit(x) __builtin_popcount(x)
#define gcd(a, b) __gcd(a, b)
#define lcm(a, b) (a*b/gcd(a, b))
int xm[4] = {-1, 1, 0, 0};
int ym[4] = {0, 0, -1, 1};
const int MOD = 1e9 + 7;
const int MAXN = 5e5 + 5;
const ll POW = 9973;

#define ld long double

int s;

bool works(ld x) {
    int sum=0;
    for(int i=0;i<(int)x;i++) {
        int z = (int) sqrt(x*x-(i+1)*(i+1));
        sum += z;
        // cout << z << " " << i+1 << endl; 

    }
    return 4*sum>=s;
}

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    ld L=0, R = 4e4;
    cin>>s;s++;
    while (R-L>1e-7) {
        ld mid = (L+R)/2;
        if (works(mid)) {
            R=mid;
        } else {
            L=mid;
        }
    }
    cout<<setprecision(9) << L << endl;
}