#include <bits/stdc++.h>
using namespace std;
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define vv(type, c, m, n, i) vector<vector<type>> c(m, vector<type>(n, i))
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a), i##_len=(n); i>i##_len; --i)
#define len(x) ((int)(x).size())
#define mp make_pair
#define eb emplace_back
#define em emplace
#define fi first
#define se second
#define get(a, i) get<i>(a)
#define mt make_tuple
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef pair<int, int> pii;
#define mini min_element
#define maxi max_element
#define sum(a, b) accumulate(a, b)
#define chmax(a,b) if(a<b)a=b
#define chmin(a,b) if(a>b)a=b
#define ce(x, y) (x + y - 1) / y
#define print(t) cout << (t) << "\n";
#define printk(v) {rep(i, 0, len(v) - 1) { cout << v[i] << " "; } cout << v.back() << endl;}
string d = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
string solve() {
	int n; cin >> n;
	string s = "";
	vi v(1200, 0);
	rrep(i, 189, -1) {
		int t = (d[i] - '0') * n;
		int j = i;
		while (t > 0) {
			v[1000 + j] = t % 10 + v[1000 + j];
			v[1000 + j - 1] += v[1000 + j] / 10;
			v[1000 + j] %= 10;
			--j;
			t /= 10;
		}
		s += (v[1000 + i] + '0');
	}
	s += '.';
	s += (v[999] + '0');
	if (v[998] != 0) s += (v[998] + '0');
	reverse(all(s));
	return s;
}
int main() {
	print(solve());
	return 0;
}