#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
typedef long long ll;
const double eps=1e-8;
int s;
bool check(double r){
    int i;
    ll cnt=0,cur;
    for(i=1;r>i;i++){
        cur=int(sqrt(r*r-i*i))*4;
        cnt+=cur;
        if(cur==0)
            break;
    }
    return cnt>s;
}
double solve(){
    double l=1,r=5e4,mid;
    while(r-l>eps){
        mid=(l+r)/2;
        if(check(mid))
            r=mid;
        else
            l=mid;
    }
    return l;
}
int main(){
    scanf("%d",&s);
    printf("%.10lf",solve());
    return 0;
}