// template version 1.15 using namespace std; #include // varibable settings #define int long long const int INF=1e18; // define basic macro {{{ #define _overload3(_1,_2,_3,name,...) name #define _rep(i,n) repi(i,0,n) #define repi(i,a,b) for(int i=(int)(a);i<(int)(b);++i) #define rep(...) _overload3(__VA_ARGS__,repi,_rep,)(__VA_ARGS__) #define _rrep(i,n) rrepi(i,0,n) #define rrepi(i,a,b) for(int i=(int)((b)-1);i>=(int)(a);--i) #define rrep(...) _overload3(__VA_ARGS__,rrepi,_rrep,)(__VA_ARGS__) #define each(i,a) for (auto&& i : a) #define all(x) (x).begin(),(x).end() #define rall(x) (x).rbegin(),(x).rend() #define sz(x) ((int)(x).size()) #define pb(a) push_back(a) #define mp(a, b) make_pair(a, b) #define mt(a, b, c) make_tuple(a, b, c) #define ub upper_bound #define lb lower_bound #define posl(A, x) (lower_bound(all(A), x)-A.begin()) #define posu(A, x) (upper_bound(all(A),x)-A.begin()) template inline void chmax(T &a, const T &b) { if((a) < (b)) (a) = (b); } template inline void chmin(T &a, const T &b) { if((a) > (b)) (a) = (b); } #define divceil(a,b) ((a)+(b)-1)/(b) #define is_in(x, a, b) ((a)<=(x) && (x)<(b)) #define uni(x) sort(all(x));x.erase(unique(all(x)),x.end()) #define slice(l, r) substr(l, r-l) typedef long long ll; typedef vector vi; typedef vector vvi; typedef long double ld; typedef pair pii; typedef tuple iii; template using PQ = priority_queue, greater>; struct Fast { Fast(){ std::cin.tie(0); ios::sync_with_stdio(false); } } fast; #if defined(PCM) || defined(LOCAL) #else #define dump(...) 42 #define dump_1d(...) 42 #define dump_2d(...) 42 #define cerrendl 42 #endif //}}} signed main() { int n,k;cin>>n>>k; double ans = (double)n*(n+1)/2 / (n+1); printf("%.12f", ans); return 0; }