#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define Pi pair<int,int>
#define IINF 1e9
#define LINF 1e18
#define vi vector<int>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 0, 1,0,-1 };
int dy[] = { 1, 0,-1,0 };

unsigned long long str_to_int(std::string str) {
	unsigned long long ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

void isPrime(ll n) {
	if (n <= 1) {
		cout << "1 1" << endl;
		return;
	}
	if (n == 2) {
		cout << "2 1" << endl;
		return;
	}
	if (n % 2 == 0){
		cout << 2 << " " << n / 2 << endl;
		return;
	}	
	for (ll i = 3; i*i <= n; i += 2) {
		if (n%i == 0) {
			cout << i << " " << n / i << endl;
			return;
		}
	}
	cout << 1 << " " << n << endl;
	return;
}

void solve() {
	string D = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
	int N;
	cin >> N;
	string ans = "";
	int flag = 1;
	for (int i = D.length() - 1; i >= 0; i--) {
		if (i == D.length() - 1) {
			string tmp = to_string(((D[i] - '0')*N));
			ans = tmp+ans;
			if (tmp.length() == 3) {
				flag = 3;
			}
		}
		else {
			int t = ((D[i] - '0')*N), sub;
			string subst, toend,tmp;
			tmp = to_string(t);
			if (flag == 3) {
				subst = ans.substr(0, 2);
				toend = ans.substr(2, ans.length() - 2);
				sub = str_to_int(subst);
				sub += t;
				ans = to_string(sub) + toend;
			}
			else if(flag == 2){
				subst = ans.substr(0, 1);
				toend = ans.substr(1, ans.length() - 1);
				sub = str_to_int(subst);
				sub += t;
				ans = to_string(sub) + toend;
			}
			else {
				ans = tmp + ans;
			}
			if (tmp.length() == 3) {
				flag = 3;
			}
			else if(tmp.length() == 2){
				flag = 2;
			}
			else {
				flag = 1;
			}
		}
	}
	if (N >= 81) {
		ans = ans.substr(0, 2) + "." + ans.substr(2, ans.length() - 2);
	}
	else if (N < 9) {
		ans = "0." + ans;
	}
	else {
		ans = ans.substr(0, 1) + "." + ans.substr(1, ans.length() - 1);
	}
	P(ans);
}

int main() {
	solve();
	return 0;
}