#define _CRT_SECURE_NO_WARNINGS
#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<random>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())




string s = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";



int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	int n,carry=0;
	string t;
	cin >> n;
	for (int i = s.size() - 1; i >= 0;i--) {
		carry += n*(s[i] - '0');
		t += carry % 10 + '0';
		carry /= 10;
	}
	reverse(all(t));

	cout << carry << '.' << t << endl;

	return 0;
}