#include "bits/stdc++.h" using namespace std; typedef long long ll; typedef unsigned long long ull; typedef vector veci; typedef vector vecll; typedef vector vecs; template using Hash=unordered_map; #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 T read(){T a;cin >> a;return a;} template void read(T& a){cin >> a;} template void read(T& a, Args&... args){cin >> a; read(args...);} template void rarr(T a, int n){for(int i = 0; i < n; i++) {cin >> a[i];}} template void write(T a){cout << setprecision(12) << a << endl;} template void write(T a, Args... args){cout << setprecision(12) << a << _SPLIT; write(args...);} template void warr(vector a, const char* c = " "){cout << a[0];for(int i = 1; i < (int)a.size(); i++)cout << c << a[i];cout << endl;;} template 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 rand1(-1, 1); uniform_int_distribution rand2(0, 1); uniform_int_distribution 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; }