#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
string D = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
int main(){
    int N; cin >> N;
    vi b(sz(D));
    rep(i, sz(D)){
        b[i] = D[i] - '0';
        b[i] *= N;
    }
    int m = 0;
    for(int i = sz(b) - 1; i >= 0; --i){
        if(i == 0)m += b[i] / 10;
        else b[i - 1] += b[i] / 10;
        b[i] %= 10;
    }
    cout << m << ".";
    each(a, b)cout << a;
    cout << endl;
}