#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

constexpr double eps = 1e-8;

int main() {
    double d;
    cin >> d;
    double res = 0;
    double y = d;
    while(std::abs(y) > eps) {
        double x = sqrt(d*d - y*y);
        if(y + eps < x) {
            break;
        }
        double tmp = y+x;
        if(x < 1 - eps) {
            for(int i=1; i<=d; ++i) {
                if(abs(y-i) < eps) {
                    tmp = y+1;
                    break;
                }
            }
        }
        res = max(res, tmp);
        y -= 0.00001;
    }
    cout << fixed << setprecision(10) << res << endl;
}
