#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    string d = "1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991";
    vector<int> vals(d.length());
    int n;
    cin >> n;

    rep(i, d.length()) {
        vals[i] = stoi(""s + d[i]) * n;
    }
    vector<int> result(d.length() + 2, 0);
    for(int i=d.length()-1; i>=0; i--) {
        result[i+2] += vals[i];
        result[i] += result[i+2] / 100;
        result[i+1] += result[i+2] % 100 / 10;
        result[i+2] %= 10;
    }
    result[0] += result[1] / 10;
    result[1] %= 10;
    rep(i, d.length()+2) {
        if(i == 0 && result[i] == 0) continue;
        if(i == 2) cout << ".";
        cout << result[i];
    }
    cout << "\n";
}