#include <bits/stdc++.h>
using namespace std;
#define _ <<" "<<
#define sz(x) ((int) (x).size())
typedef pair<int, int> pii;
typedef long long ll;
const int maxn = 1e5 + 5;

const long double eps = 1e-13;
int n, m;
ll s; 

bool check(long double x) {
    if (x >= maxn) return true;
    ll cur = 0;
    for (ll i = 1;i <= x; ++i) {
        cur += (int)sqrt(x*x - i*i); 
    }
    cur *= 4;
    return cur >= s;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> s;
    long double L = 1, R = INT_MAX;
    while (R-L > eps) {
        long double M = (L+R)/2;
        if (check(M)) R = M;
        else L = M;
    }
    cout << fixed << setprecision(8) << L << '\n';
    return 0;
}