WRONG

#include <bits/stdc++.h>

typedef int64_t Int;

int main() {
    Int nCandy, nMan, maxX, maxCountPerMan;
    std::cin >> nCandy >> nMan >> maxX >> maxCountPerMan;

    Int answ = 0;
    for (Int countPerMan = 1; countPerMan <= maxCountPerMan; ++countPerMan) {

        std::function<Int(Int)> calcAnsw = [&](Int x) {
            return x > maxX ? 0 : x * ((nCandy + x * nMan-1) / (x * nMan));
        };

        std::function<Int(Int)> calcPerMan = [&](Int x) {
            return (nCandy - nCandy % x + nMan*x-1) / (nMan * x);
        };

        // Какой x выбрать чтобы Аркадий получил на руки ровно countPerMan раз
        // countPerMan * x * k >= nCandy
        Int x = (nCandy + countPerMan * nMan-1) / (countPerMan * nMan);
        //std::cout << "countPerMan = " << countPerMan << ", x = " << x << std::endl;
        answ = std::max(answ, calcAnsw(x));
        // Бинпоиск на x:
        Int low = x+1, high = nCandy+1;
        while (high - low > 1) {
            Int mid = (high + low) / 2;
            if (calcPerMan(mid) == countPerMan) {
                low = mid;
            } else {
                high = mid;
            }
        }
        if (calcPerMan(low) == countPerMan) {
            answ = std::max(answ, calcAnsw(low));
        }
    }
    assert(answ != 0);
    std::cout << answ << std::endl;

    return 0;
}