#include <iostream>
#include <vector>
#include <queue>
#include <string>
#include <list>
#include <set>
#include <map>
#include <sstream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cstdio>

using namespace std;



#define clr(x) memset(x, 0, sizeof(x))


class TheArray
{
        public:
        int find(int n, int d, int first, int last);
        
// BEGIN CUT HERE
	public:
	void run_test(int Case) { if ((Case == -1) || (Case == 0)) test_case_0(); if ((Case == -1) || (Case == 1)) test_case_1(); if ((Case == -1) || (Case == 2)) test_case_2(); if ((Case == -1) || (Case == 3)) test_case_3(); if ((Case == -1) || (Case == 4)) test_case_4(); }
	private:
	template <typename T> string print_array(const vector<T> &V) { ostringstream os; os << "{ "; for (typename vector<T>::const_iterator iter = V.begin(); iter != V.end(); ++iter) os << '\"' << *iter << "\","; os << " }"; return os.str(); }
	void verify_case(int Case, const int &Expected, const int &Received) { cerr << "Test Case #" << Case << "..."; if (Expected == Received) cerr << "PASSED" << endl; else { cerr << "FAILED" << endl; cerr << "\tExpected: \"" << Expected << '\"' << endl; cerr << "\tReceived: \"" << Received << '\"' << endl; } }
	void test_case_0() { int Arg0 = 3; int Arg1 = 5; int Arg2 = 2; int Arg3 = 4; int Arg4 = 7; verify_case(0, Arg4, find(Arg0, Arg1, Arg2, Arg3)); }
	void test_case_1() { int Arg0 = 10; int Arg1 = 100; int Arg2 = 999; int Arg3 = 100; int Arg4 = 999; verify_case(1, Arg4, find(Arg0, Arg1, Arg2, Arg3)); }
	void test_case_2() { int Arg0 = 1000000; int Arg1 = 0; int Arg2 = 474; int Arg3 = 474; int Arg4 = 474; verify_case(2, Arg4, find(Arg0, Arg1, Arg2, Arg3)); }
	void test_case_3() { int Arg0 = 97; int Arg1 = 53; int Arg2 = -92; int Arg3 = 441; int Arg4 = 2717; verify_case(3, Arg4, find(Arg0, Arg1, Arg2, Arg3)); }
	void test_case_4() { int Arg0 = 99; int Arg1 = 3; int Arg2 = -743; int Arg3 = -619; int Arg4 = -535; verify_case(4, Arg4, find(Arg0, Arg1, Arg2, Arg3)); }

// END CUT HERE

};


int f (int llow, int lup, int rlow, int rup) {
	if (lup < rlow || rup < llow) return -1100000011;
	return min (lup, rup);
}
int TheArray::find(int n, int d, int A, int B)
{
	int i, j, k;
	int ans = -1100000011;
	for (i = 0; i < n; ++i) {
		int j = n - 1 - i;
		ans = max (ans, f (A - d * i, A + d * i, B - j * d, B + j * d));
	}
	return ans;
}

// BEGIN CUT HERE
int main()
{
        TheArray ___test;
        ___test.run_test(-1);
        return 0;
}
// END CUT HERE