#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>

#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for(int (i) = (a)-1; (i) >= 0; (i)--)
#define FORR(i, a, b) for(int (i) = (a)-1; (i) >= (b); (i)--)
#define PI acos(-1.0)
#define DEBUG(C) cerr << C << endl;
#define VI vector <int>
#define VII vector <VI>
#define VL vector <LL>
#define VLL vector <VL>
#define VD vector <double>
#define VDD vector <VD>
#define PII pair <int, int>
#define PDD pair <double, double>
#define PLL pair <LL, LL>
#define VPII vector <PII>
#define ALL(a) (a).begin(), (a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define EB emplace_back
#define FORE(a, b) for (auto &&a:b)
#define FIND(s, n) (s.find(n) != s.end())

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

int main(void) {
    string D = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
    VI a(D.size());
    int N; cin >> N;
    int su = 0;
    REP(i, D.size()) {
	a[i] = D[i] - '0';
	a[i] *= N;
    }
    RREP(i, D.size()) {
	if (a[i] >= 100) {
	    int buf = a[i];
	    a[i] %= 10;
	    if (i > 1) {
		a[i - 2] += buf / 100;
		a[i - 1] += (buf % 100) / 10;
	    } else if (i == 1) {
		su += (buf / 100);
		a[i - 1] += (buf % 100) / 10;
	    } else {
		su += (buf / 100) * 10;
		su += (buf % 100) / 10;
	    }
	} else if (a[i] >= 10) {
	    int buf = a[i];
	    a[i] %= 10;
	    if (i) {
		a[i - 1] += buf / 10;
	    } else {
		su += buf / 10;
	    }
	}
    }
    cout << su << ".";
    REP(i, a.size()) {
	cout << a[i];
    }
    cout << endl;
    return 0;
}