import std.stdio, std.string, std.conv, std.range; import std.algorithm, std.array, std.typecons, std.container; import std.math, std.numeric, std.random, core.bitop; enum inf = 1_001_001_001; enum infl = 1_001_001_001_001_001_001L; enum mod = 1_000_000_007L; void main() { int N, K; scan(N, K); if (K > N) { writeln(-1); return; } writeln(K - 1); } void scan(T...)(ref T args) { import std.stdio : readln; import std.algorithm : splitter; import std.conv : to; import std.range.primitives; auto line = readln().splitter(); foreach (ref arg; args) { arg = line.front.to!(typeof(arg)); line.popFront(); } assert(line.empty); } void fillAll(R, T)(ref R arr, T value) { static if (is(typeof(arr[] = value))) { arr[] = value; } else { foreach (ref e; arr) { fillAll(e, value); } } } bool chmin(T, U...)(ref T x, U args) { bool isChanged; foreach (arg; args) { if (x > arg) { x = arg; isChanged = true; } } return isChanged; } bool chmax(T, U...)(ref T x, U args) { bool isChanged; foreach (arg; args) { if (x < arg) { x = arg; isChanged = true; } } return isChanged; }