import std.stdio, std.array, std.string, std.conv, std.algorithm; import std.typecons, std.range, std.random, std.math, std.container; import std.numeric, std.bigint, core.bitop; int point(int star, int rank) { return 50 * star + 500 * star / (8 + 2 * rank); } void main() { auto s = readln.split.map!(to!int); auto N = s[0]; auto S = s[1]; auto W = s[2]; auto A = readln.split.map!(to!int).array; auto WP = A[W] + 100 * S; A = A[0..W] ~ A[W+1..N]; N -= 1; auto numerator = new int[](N); foreach (i; 0..N) { int hi = N + 1; int lo = 0; while (hi - lo > 1) { auto mid = (hi + lo) / 2; //writeln(i, " ", hi, " ", lo, " " , A[i] + point(S, mid)); if (A[i] + point(S, mid) > WP) lo = mid; else hi = mid; } numerator[i] = N + 1 - hi; } numerator.sort(); foreach (i; 0..N) { numerator[i] -= i; if (numerator[i] <= 0) { writeln(0.0); return; } } real ans = 1.0L; foreach (i; 0..N) ans = ans * numerator[i] / (i + 1); writefln("%.9f", ans); }