#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

typedef int64_t s64;
typedef uint64_t u64;

int n;
s64 max;
#define INF 1000000000000000000


namespace DP {
	s64 run(s64 median, s64 mode) {
		std::vector<std::vector<std::vector<s64> > > dp(n + 1,
			std::vector<std::vector<s64> > (2 * max * n + 1, std::vector<s64> (n + 1, -INF)));
		dp[0][max * n][0] = 0;
		for (int i = 0; i <= max; i++) {
			for (int j = n; j >= 0; j--) {
				for (int k = 0; k <= 2 * max * n; k++) {
					for (int l = 0; l <= n; l++) {
						if (dp[j][k][l] == -INF) continue;
						for (int m = 1; j + m <= n; m++) {
							if (j <= n / 2 && j + m > n / 2 && i != median) continue;
							int next_k = k;
							if (m == l) next_k += (i - mode) * m;
							else if (m > l) next_k = max * n + (i - mode) * m;
							dp[j + m][next_k][std::max(l, m)] = std::max(dp[j + m][next_k][std::max(l, m)], dp[j][k][l] + i * m);
						}
					}
				}
			}
		}
		s64 res = -1;
		for (int i = 1; i <= n; i++) res = std::max(res, dp[n][max * n][i]);
		return res;
	}
};




namespace Gu {
	s64 calc(int mode_num, s64 mode_sum, int mode_freq, s64 min, s64 max, int all_num) {
		assert(mode_freq > 1);
		int other = all_num - mode_num * mode_freq;
		assert(other >= 0);
		if (!mode_num) {
			if (!mode_sum) {
				int other_block = other / (mode_freq - 1);
				int other_leftover = other % (mode_freq - 1);
				if (other_block + !!other_leftover > max - min + 1) return -INF;
				return other_block * (max + max - other_block + 1) / 2 * (mode_freq - 1) + other_leftover * (max - other_block);
			}
			return -INF; // invalid
		}
		if (max - min + 1 < mode_num) return -INF;
		s64 clearance = mode_sum - mode_num * (min + min + mode_num - 1) / 2;
		if (clearance < 0) return -INF;
		if (mode_num * (max + max - mode_num + 1) / 2 < mode_sum) return -INF;
		int other_block = other / (mode_freq - 1);
		int other_leftover = other % (mode_freq - 1);
		if (other_block && !other_leftover) other_block--, other_leftover = mode_freq - 1;
		if (other_block + !!other_leftover + mode_num > max - min + 1) return -INF;
		int number_clearance = max - min + 1 - (other_block + !!other_leftover + mode_num);
		int slide = clearance / mode_num - number_clearance;
		s64 sum = mode_sum * mode_freq + other_block * (max + max - other_block + 1) / 2 * (mode_freq - 1)
			+ other_leftover * (max - other_block);
		if (slide > 0) {
			sum -= (other_leftover + (s64) (mode_freq - 1) * (slide - 1)) * mode_num;
			sum -= clearance % mode_num * (mode_freq - 1);
		} else if (!slide) sum -= clearance % mode_num * other_leftover;
		return sum;
	}
	s64 run(s64 median, s64 mode) {
		int half = n / 2;
		s64 upper = max - median;
		s64 res = -1;
		// freq == 1
		if (median >= half && median + half <= max) {
			s64 min_sum = median + (s64) (half - 1) * half / 2 + (s64) (median + 1 + median + half) * half / 2;
			s64 max_sum = median + (s64) (median - 1 + median - half) * half / 2 + (s64) (max + max - half + 1) * half / 2;
			if (mode * n >= min_sum && mode * n <= max_sum) res = mode * n;
		}
		for (int freq = 2; freq <= n; freq++) {
			for (int left = 0; left * freq <= half && left <= median; left++) {
				for (int right = 0; right * freq <= half && right <= upper; right++) {
					int median_l_min = left * freq;
					int median_l_max = std::min<s64>(half, left * freq + (median - left) * (freq - 1));
					int median_r_max = n - right * freq;
					int median_r_min = std::max<s64>(half + 1, n - right * freq - (upper - right) * (freq - 1));
					assert(median_l_min <= median_l_max);
					assert(median_r_min <= median_r_max);
					// std::cerr << freq << " " << left << "," << right << std::endl;
					if (left || right) { // don't use median as (one of) mode(s)
						s64 mode_all_sum = mode * (left + right);
						int median_r = median_r_min;
						int median_l = std::max(median_l_min, median_r - (freq - 1));
						if (median_l <= half) {
							// if (freq == 3 && left == 0 && right == 1) std::cerr << "yay:" << median_l_max << std::endl;
							assert(median_r > half);
							for (s64 left_sum = 0; left_sum <= mode_all_sum; left_sum++) {
								s64 cur = (median_r - median_l) * median;
								cur += calc(left, left_sum, freq, 0, median - 1, median_l);
								cur += calc(right, mode_all_sum - left_sum, freq, median + 1, max, n - median_r);
								res = std::max(res, cur);
							}
						}
					}
					{ // use median as (one of) mode(s)
						median_l_min = std::max(median_l_min, median_r_min - freq);
						median_l_max = std::min(median_l_max, median_r_max - freq);
						if (median_l_max >= median_l_min) {
							int median_l = median_l_min;
							assert(median_l <= half);
							assert(median_l + freq > half);
							s64 mode_all_sum = mode * (left + right + 1) - median;
							for (s64 left_sum = 0; left_sum <= mode_all_sum; left_sum++) {
								s64 cur = freq * median;
								cur += calc(left, left_sum, freq, 0, median - 1, median_l);
								cur += calc(right, mode_all_sum - left_sum, freq, median + 1, max, n - median_l - freq);
								res = std::max(res, cur);
							}
						}
					}
				}
			}
		}
		return res;
	}
};



// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------
// ----------------------------------------------------------------------------------------


namespace Fast {
	// max of sum of an array consisting of exactly all_num integers each in [min, max]
	//   that has exactly mode_num modes
	//      and they appear exactly mode_freq times each
	//      and sum of them(unique ones) equals to mode_sum
	// -INF if no such array exists
	// O(1)
	s64 calc(int mode_num, s64 mode_sum, int mode_freq, s64 min, s64 max, int all_num) {
		assert(mode_freq > 1);
		int other = all_num - mode_num * mode_freq;
		assert(other >= 0);
		if (!mode_num) {
			if (!mode_sum) {
				int other_block = other / (mode_freq - 1);
				int other_leftover = other % (mode_freq - 1);
				if (other_block + !!other_leftover > max - min + 1) return -INF;
				return other_block * (max + max - other_block + 1) / 2 * (mode_freq - 1) + other_leftover * (max - other_block);
			}
			return -INF; // invalid
		}
		if (max - min + 1 < mode_num) return -INF;
		s64 adding = mode_sum - mode_num * (min + min + mode_num - 1) / 2;
		if (adding < 0) return -INF;
		if (mode_num * (max + max - mode_num + 1) / 2 < mode_sum) return -INF;
		int other_block = other / (mode_freq - 1);
		int other_leftover = other % (mode_freq - 1);
		if (other_block && !other_leftover) other_block--, other_leftover = mode_freq - 1;
		if (other_block + !!other_leftover + mode_num > max - min + 1) return -INF;
		int default_clearance = max - min + 1 - (other_block + !!other_leftover + mode_num);
		int slide = adding / mode_num - default_clearance;
		s64 sum = mode_sum * mode_freq + other_block * (max + max - other_block + 1) / 2 * (mode_freq - 1)
			+ other_leftover * (max - other_block);
		if (slide > 0) {
			sum -= (other_leftover + (s64) (mode_freq - 1) * (slide - 1)) * mode_num;
			sum -= adding % mode_num * (mode_freq - 1);
		} else if (!slide) sum -= adding % mode_num * other_leftover;
		return sum;
	}
	s64 get_candidate(int mode_num, int mode_freq, s64 max, int all_num) {
		assert(mode_freq > 1);
		int other = all_num - mode_num * mode_freq;
		assert(other >= 0);
		if (!mode_num) return 0;
		
		int other_used = other / (mode_freq - 1);
		if (other % (mode_freq - 1)) other_used++;
		
		return (s64) (max - other_used + max - other_used - mode_num + 1) * mode_num / 2;
	}
	// max of sum of a non-decreasing array a consisting of exactly n integers each in [0, max] such that
	//   its median is median and it occupies exactly a[median_l, median_r)
	//   and there are exactly left modes in a[0, median_l) and exactly right modes in a[median_r, n)
	//     and their unique sum equals to mode_all_sum(the median itself as a mode does not count)
	//     and they appear exactly freq times each
	// -1 if no such array exists
	// O(1)
	s64 solve_sub(s64 median, int median_l, int median_r, int freq, s64 mode_all_sum, int left, int right) {
		s64 lower = 0, upper = mode_all_sum; // lower and upper bound(both inclusive) of sum of modes on the left side
		lower = std::max(lower, (s64) (left - 1) * left / 2);
		upper = std::min(upper, (s64) (median - 1 + median - left) * left / 2);
		lower = std::max(lower, mode_all_sum - (s64) (max + max - right + 1) * right / 2);
		upper = std::min(upper, mode_all_sum - (s64) (median + 1 + median + right) * right / 2);
		
		std::vector<s64> candidates{lower, upper};
		candidates.push_back(get_candidate(left, freq, median - 1, median_l));
		candidates.push_back(candidates.back() + left);
		candidates.push_back(mode_all_sum - get_candidate(right, freq, max, n - median_r));
		candidates.push_back(candidates.back() - right);
		s64 res = -1;
		for (auto left_sum : candidates) if (left_sum >= lower && left_sum <= upper) {
			s64 cur = (median_r - median_l) * median;
			cur += calc(left, left_sum, freq, 0, median - 1, median_l);
			cur += calc(right, mode_all_sum - left_sum, freq, median + 1, max, n - median_r);
			res = std::max(res, cur);
		}
		return res;
	}
	s64 run(s64 median, s64 mode) {
		assert(n & 1);
		int half = n / 2;
		s64 upper = max - median;
		s64 res = -1;
		// freq == 1
		if (median >= half && median + half <= max) {
			s64 min_sum = median + (s64) (half - 1) * half / 2 + (s64) (median + 1 + median + half) * half / 2;
			s64 max_sum = median + (s64) (median - 1 + median - half) * half / 2 + (s64) (max + max - half + 1) * half / 2;
			if (mode * n >= min_sum && mode * n <= max_sum) res = mode * n;
		}
		for (int freq = 2; freq <= n; freq++) {
			for (int left = 0; left * freq <= half && left <= median; left++) {
				for (int right = 0; right * freq <= half && right <= upper; right++) {
					int median_l_min = left * freq;
					int median_l_max = std::min<s64>(half, left * freq + (median - left) * (freq - 1));
					int median_r_max = n - right * freq;
					int median_r_min = std::max<s64>(half + 1, n - right * freq - (upper - right) * (freq - 1));
					assert(median_l_min <= median_l_max);
					assert(median_r_min <= median_r_max);
					// std::cerr << freq << " " << left << "," << right << std::endl;
					if (left || right) { // don't use median as (one of) mode(s)
						s64 mode_all_sum = mode * (left + right);
						int median_r = median_r_min;
						int median_l = std::max(median_l_min, median_r - (freq - 1));
						if (median_l <= half) {
							assert(median_r > half);
							res = std::max(res, solve_sub(median, median_l, median_r, freq, mode_all_sum, left, right));
						}
					}
					{ // use median as (one of) mode(s)
						median_l_min = std::max(median_l_min, median_r_min - freq);
						median_l_max = std::min(median_l_max, median_r_max - freq);
						if (median_l_max >= median_l_min) {
							int median_l = median_l_min;
							assert(median_l <= half);
							assert(median_l + freq > half);
							s64 mode_all_sum = mode * (left + right + 1) - median;
							res = std::max(res, solve_sub(median, median_l, median_l + freq, freq, mode_all_sum, left, right));
						}
					}
				}
			}
		}
		return res;
	}
};

bool random_check() {
	std::random_device rnd_dev;
	std::mt19937 rnd(rnd_dev() ^ clock());
	for (int median = 0; median <= max; median++) {
		for (int mode = 0; mode <= max; mode++) {
			int r0 = Gu::run(median, mode);
			int r1 = Fast::run(median, mode);
			if (r0 != r1) {
				std::cerr << "!!!!! FAILED !!!!!" << std::endl;
				std::cerr << n << " " << max << " " << median << " " << mode << std::endl;
				std::cerr << "correct:" << r0 << " wrong:" << r1 << std::endl;
				std::cerr << std::endl;
				return false;
			}
		}
	}
	return true;
}
void random_check_all() {
	int n_local = n;
	for (n = 1; n <= n_local; n += 2) random_check();
}

int main() {
	for (int i = 0; i < 10; i++) {
		n = ri();
		max = ri();
		int median = ri();
		int mode = ri();
		printf("%" PRId64 "\n", Fast::run(median, mode));
	}
	return 0;
}