import std.algorithm;
import std.range;
import std.stdio;
import std.math;
import std.array;
import std.string;
import std.conv;

/// 数列の読み込み
auto readNums(T = int)() {
	return readln().chomp.split.map!(to!T).array;
}

/// 数の読み込み
auto readNum(T = int)() {
	return readNums!T.front;
}

/// 指定行数読み込み
auto readRows(size_t rows) {
	return generate(() => readln().chomp).take(rows).array;
}

/// 範囲の計算
auto range(T)(T a, T b, T c, T d) {
    auto start = max(a, c);
    auto end = max(b, d);
    return (start < end) ? tuple(start, end) : tuple(cast(T) 0, cast(T) 0);
}

auto maxElement(R)(R r) {
    return r.reduce!((a, b) => max(a, b));
}

auto minElement(R)(R r) {
    return r.reduce!((a, b) => min(a, b));
}

auto minIndex(T)(T[] r) {
    return r.length - r.minPos.length;
}

void main() {
    const nk = readNums();
    immutable n = nk[0];
    immutable k = nk[1] - 1;
    const nums = readNums();
    
    writefln("%d", (n + (k - 1)) / k);
}
