#include<bits/stdc++.h>
#define Add(x,y) (x+y>=mod)?(x+y-mod):(x+y)
#define lowbit(x) x&(-x)
#define pi pair<ll,ll>
#define pii pair<ll,pair<ll,ll>>
#define iip pair<pair<ll,ll>,ll>
#define ppii pair<pair<ll,ll>,pair<ll,ll>>
#define fi first
#define se second
#define full(l,r,x) for(auto it=l;it!=r;it++) (*it)=x
#define Full(a) memset(a,0,sizeof(a))
#define open(s1,s2) freopen(s1,"r",stdin),freopen(s2,"w",stdout);
#define For(i,l,r) for(int i=l;i<=r;i++)
#define _For(i,l,r) for(int i=r;i>=l;i--)
using namespace std;
typedef long double lb;
typedef double db;
typedef unsigned long long ull;
typedef long long ll;
bool Begin;
const ll N=55;
inline ll read(){
    ll x=0,f=1;
    char c=getchar();
    while(c<'0'||c>'9'){
        if(c=='-')
          f=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9'){
        x=(x<<1)+(x<<3)+(c^48);
        c=getchar();
    }
    return x*f;
}
inline void write(ll x){
	if(x<0){
		putchar('-');
		x=-x;
	}
	if(x>9)
	  write(x/10);
	putchar(x%10+'0');
}
ll n;
lb dp[N];
bool End;
int main(){
  n=read();
  dp[1]=1,dp[2]=2;
  For(i,3,n){
    lb s=0;
    For(j,1,i-1)
      For(k,j+1,i-1)
        s+=j*k;
    s/=((i-1)*(i-2))/2;
    dp[i]=dp[i-1]+(s*(i-2)+2)/i;
  }
  printf("%.10Lf\n",dp[n]);
	//cerr<<'\n'<<abs(&Begin-&End)/1048576<<"MB";
	return 0;
}