#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0; i<(int)n; i++)
#define rep1(i,n) for(int i=1; i<(int)n; i++)
#define repa(i,a,n) for(int i=(a); i<(int)(n); i++)
#define all(vec) vec.begin(),vec.end()
#define COUT(x) cout<<(x)<<endl
#define YES(x) cout<<(x?"YES":"NO")<<endl
#define Yes(x) cout<<(x?"Yes":"No")<<endl
#define F first
#define S second
using vi = vector<int>;
using vs = vector<string>;
using vvi = vector<vi>;
using pii = pair<int, int>;
using vpii = vector<pii>;
const int dx[4] = {1, 0,-1, 0};
const int dy[4] = {0, 1, 0,-1};
int gcd(int a, int b){if(a%b == 0){return(b);}else{return(gcd(b, a%b));}}
int lcm(int a, int b){return a/gcd(a, b)*b;}
template <typename T> bool chmax(T &a,const T& b){if(a<b){a=b;return true;}return false;}
template <typename T> bool chmin(T &a,const T& b){if(a>b){a=b;return true;}return false;}
//cout << fixed << setprecision(15);
int N, M, K, H, W, X, Y;
string S,T;
const int INF = 1e18;
const int mod = 1e9+7;

signed main(){
    double k; cin >> k;
    double ans = 0;
    double n = 1;
    while(1){
        double t = 1/(n*(n+k));
        ans += 1/(n*(n+k));
        if(t < 1e-15) break;
        n++;
    } 
    cout << fixed << setprecision(15);
    COUT(ans);
    return 0;
}