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

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> veci;
typedef vector<ll> vecll;
typedef vector<string> vecs;
template<class T,class U> using Hash=unordered_map<T,U>;
 
#define REP(i, a, n) for(ll i = a; i < (ll)(n); i++)
#define RREP(i, a, n) for(ll i = n-1; i >= (ll)(a); i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define MD 1000000007
#define _SPLIT " "
 
template<class T> T read(){T a;cin >> a;return a;}
template<class T> void read(T& a){cin >> a;}
template<class T,class ...Args> void read(T& a, Args&... args){cin >> a; read(args...);} 
template<class T> void rarr(T a, int n){for(int i = 0; i < n; i++) {cin >> a[i];}}
template<class T> void write(T a){cout << setprecision(12) << a << endl;}
template<class T,class ...Args> void write(T a, Args... args){cout << setprecision(12) << a << _SPLIT; write(args...);}
template<class T> void warr(vector<T> a, const char* c = " "){cout << a[0];for(int i = 1; i < (int)a.size(); i++)cout << c << a[i];cout << endl;;}
template<class T> void warr(T a, int n, const char* c = " "){cout << a[0];for(int i = 1; i < n; i++)cout << c << a[i];cout << endl;}
void split(string s, string delim, veci& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(atoi(s.substr(pos).data()));break;}else {result.push_back(atoi(s.substr(pos, p - pos).data()));}pos = p + delim.size();}}
void split(string s, string delim, vecs& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(s.substr(pos));break;}else {result.push_back(s.substr(pos, p - pos));}pos = p + delim.size();}}
ll gcd(ll a, ll b){while(true){ll k = a % b;if(k == 0)return b;a = b;b = k;}}
ll comb(ll n, ll m){ll p=1;m=min(m,n-m);for(ll i=1;i<=m;i++){p*=n-i+1;p/=i;}return p;}

int main(void)
{
    random_device rnd;
    mt19937 mt(rnd());
    uniform_int_distribution<int> rand1(-1, 1);
    uniform_int_distribution<int> rand2(0, 1);
    uniform_int_distribution<int> rand100(1, 100);
    int sp,k;
    read(sp,k);
    int win=0;
    int ct=0;
    while(ct<1e8){
        int bef=-1;
        int jd=0;
        int p=sp;
        while(jd==0){
            if(bef==0){
                int t=rand100(mt);
                if(t<=p){
                    jd=rand2(mt);
                    p=max(0,p-k);
                }
                else{
                    jd=rand1(mt);
                    p=min(100,p+k);
                }
            }
            else jd=rand1(mt);
            bef=jd;
        }
        if(jd==1)win++;
        ct++;
    }
    write((double)win/ct);
    return 0;
}