#pragma GCC optimize("Ofast","unroll-loops","omit-frame-pointer","inline")
#pragma GCC option("arch=native","tune=native","no-zero-upper")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2")
#pragma GCC optimize(3)
#include<bits/stdc++.h>
#define LL long long
#define eps 1e-8
#define rep(i,l,r) for(int i=l;i<=r;i++)
#define drep(i,r,l) for(int i=r;i>=l;i--)
using namespace std;
int rd() {
	int res=0,f=1;char ch=getchar();
	while(ch<'0'||ch>'9') {if(ch=='-') f*=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') res=(res<<1)+(res<<3)+(ch^48),ch=getchar();
	return res*f;
}
int s;
LL check(double mid) {
	LL ans=0;
	for(int i=0;i+1<=mid;i++) {
		ans+=floor(sqrt(mid*mid-1.0*(i+1)*(i+1)));
	}
	return ans*4;
}
int main() {
//	cout<<"FUCK "<<check(5)<<endl;
	s=rd();
	double l=0,r=100000,mid;
	while(r-l>eps) {
		mid=(l+r)/2;
		if(check(mid)>s) r=mid;
		else l=mid;
	}
	printf("%.8lf",l);
	return 0;
}