#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
static const int INF = 0x3f3f3f3f; static const long long INFL = 0x3f3f3f3f3f3f3f3fLL;
typedef vector<int> vi; typedef pair<int, int> pii; typedef vector<pair<int, int> > vpii; typedef long long ll;
template<typename T, typename U> static void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> static void amax(T &x, U y) { if(x < y) x = y; }

int main() {
	string x = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
	reverse(x.begin(), x.end());
	int N;
	while(~scanf("%d", &N)) {
		string r;
		int carry = 0;
		rep(i, x.size()) {
			int d = x[i] - '0';
			int x = d * N + carry;
			r += char('0' + x % 10);
			carry = x / 10;
		}
		r += '.';
		do {
			r += char('0' + carry % 10);
			carry /= 10;
		} while(carry != 0);
		reverse(r.begin(), r.end());
		puts(r.c_str());
	}
	return 0;
}