#include<bits/stdc++.h>
using namespace std;

using lnt = long long;
using Real = long double;

#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define REP(i, n) for(lnt i=0;i<(n);++i)
#define RANGE(i, a, b) for(lnt i=(a);i<(b);++i)
#define RREP(i, n) for(lnt i=(n)-1;i>= 0;--i)

#define ln '\n'
#define pb push_back
#define eb emplace_back
#define pque priority_queue
#define umap unordered_map
#define uset unordered_set
#define dcout cout<<fixed<<setprecision(20)
#define summon_tourist cin.tie(0);ios::sync_with_stdio(false)

constexpr int dx[]={1,0,-1,0,1,1,-1,-1}, dy[]={0,-1,0,1,1,-1,1,-1};
constexpr Real eps = 1e-9; const Real pi = acosl(-1);
constexpr lnt BIG = INT_MAX/10, BBIG = LLONG_MAX/10;

template<class T> inline T GCD(T a,T b){T c;while(b!=0){c=a%b;a=b;b=c;}return a;}
template<class T> inline T LCM(T a,T b){T c=GCD(a,b);a/=c;return a*b;}
template<class T> inline T nCr(T a,T b){T i,r=1;for(i=1;i<=b;i++){r*=(a+1-i);r/=i;}return r;}
template<class T> inline T nHr(T a,T b){return nCr(a+b-1,b);}
template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

using pint = pair<int, int>; using plnt = pair<lnt, lnt>;
using vint = vector<int>; using vlnt = vector<lnt>;
constexpr lnt MOD = 1e9+7;

int main(){
    summon_tourist;

	Real N, K; cin >> N >> K;
    Real sum = (1.0+N) * N / 2.0;
    dcout << sum / (N+1) << ln;
}