#include <bits/stdc++.h>
  
using namespace std;
  
#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for(int i=(int)(s-1); i>=(int)(e); i--)
#define pb push_back
#define all(r) r.begin(),r.end()
#define rall(r) r.rbegin(),r.rend()
#define fi first
#define se second
  
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
 
const int INF = 1e9;
const ll MOD = 1e9 + 7;
double EPS = 1e-10;

using D = double;

int main(){
    D d;
    scanf("%lf", &d);
    D ans = d;
    ans = max(ans, sqrt(2)*d);
    REP(y, 1, (int)(d + EPS)+1) {
        D x = sqrt(d*d-y*y);
        ans = max(ans, max(x, 1.0)+y);
    }
    printf("%.15lf\n", ans);
    return 0;
}
