#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long long ll; #define sz size() #define pb push_back #define mp make_pair #define fi first #define se second #define all(c) (c).begin(), (c).end() #define rep(i,a,b) for(ll i=(a);i<(b);++i) #define per(i,a,b) for(ll i=b-1LL;i>=(a);--i) #define clr(a, b) memset((a), (b) ,sizeof(a)) #define ctos(c) string(1,c) #define print(x) cout<<#x<<" = "<>n>>k; assert(1<=n&&n<=100000); assert(1<=k&&k<=100000); printf("%20.20f\n", 1.*n*(n+1)/2/(n+1)); return 0; }