import java.math.*;
import java.util.*;
import java.io.*;
  
public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;



    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }

    void swap(char[]ary, int i, int j)
    {
        char t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    long readLong() throws Exception
    {
        return Long.valueOf(in.readLine());
    }

    long[] toLongArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        long[] ary = new long[n];
        for(int i = 0; i < n; i++) ary[i] = Long.valueOf(sp[i]);
        return ary;
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");
        char[] gg = in.readLine().toCharArray();}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        // char[] c = new char[4];
        // c[1] = '.';
        // for(char i = '0'; i <= '9'; i++)
        // {
        //     for(char j = '0'; j <= '9'; j++)
        //     {
        //         for(char k = '0'; k <= '9'; k++)
        //         {
        //             c[0] = i;
        //             c[2] = j;
        //             c[3] = k;
        //             double d = Double.valueOf(String.valueOf(c));
        //             int v = (int)(d * 100);
        //             String s1 = String.valueOf("" + c[0] + c[2] + c[3]),
        //                 s2 = String.valueOf(v);
        //             System.out.printf("%s %s %b\n", s1, s2, s1.equals(s2));
        //         }
        //     }
        // }


        new Main().b();
        out.flush();
    }
    void f() throws Exception
    {
      

    }

    void e() throws Exception
    {
        int[] ary = toIntArray();
        int h = ary[0], w = ary[1], m = ary[2];
        int[][] bomb = new int[m][];
        for(int i = 0; i < m; i++)
        {
            bomb[i] = toIntArray();
        }

        int ans1 = rowThenCol(bomb);
        int ans2 = colThenRow(bomb);
        out.println(Math.max(ans1, ans2));
    }

    int colThenRow(int[][] bomb)
    {
        Map<Integer, Integer> row = new HashMap<>(),
            col = new HashMap<>();
        for(int[] b : bomb)
        {
            int r = b[0], c = b[1];
            col.put(c, col.getOrDefault(c, 0) + 1);
        }
        
        int pickCol = maxKey(col);
        for(int[] b : bomb)
        {
            int r = b[0], c = b[1];
            if(pickCol == c) continue;
            row.put(r, row.getOrDefault(r, 0) + 1);
        }
        int pickRow = maxKey(row);
        return row.get(pickRow) + col.get(pickCol);
    }

    int rowThenCol(int[][] bomb)
    {
        Map<Integer, Integer> row = new HashMap<>(),
            col = new HashMap<>();
        for(int[] b : bomb)
        {
            int r = b[0], c = b[1];
            row.put(r, row.getOrDefault(r, 0) + 1);
        }
        
        int pickRow = maxKey(row);
        for(int[] b : bomb)
        {
            int r = b[0], c = b[1];
            if(pickRow == r) continue;
            col.put(c, col.getOrDefault(c, 0) + 1);
        }
        int pickCol = maxKey(col);
        return row.get(pickRow) + col.get(pickCol);
    }

    int maxKey(Map<Integer, Integer> map)
    {
        int ans = 0, freq = 0;
        for(int key : map.keySet())
        {
            if(freq < map.get(key))
            {
                ans = key;
                freq = map.get(key);
            }
        }
        return ans;
    }

    int numCut(int[] ary, int thres)
    {
        int count = 0;
        for(int v : ary)
        {
            if(v > thres)
            count += v / thres;
            // count += v % thres > 0 ? 1 : 0;
        }
        return count;
    }

    void d() throws Exception
    {
        int[] ary = toIntArray();
        int h = ary[0], w = ary[1];
        ary = toIntArray();
        int ch = ary[0] - 1, cw = ary[1] - 1;
        ary = toIntArray();
        int dh = ary[0] - 1, dw = ary[1] - 1;
        char[][] grid = new char[h][w];
        for(int i = 0; i < h; i++)
        {
            grid[i] = in.readLine().toCharArray();
        }

        int[][] dp = new int[h][w];
        int inf = 1 << 30;
        for(int[] row : dp) Arrays.fill(row, inf);
        Queue<int[]> q = new LinkedList<>();
        q.offer(new int[]{ch, cw, 0});
        int[] dx = {1, 0, -1, 0}, dy = {0, 1, 0, -1};
        dp[ch][cw] = 0;
        while(!q.isEmpty())
        {
            Queue<int[]> q2 = new LinkedList<>();
            while(!q.isEmpty())
            {
                int[] cur = q.poll();
                q2.offer(cur);
                // System.out.println(Arrays.toString(cur));
                int x = cur[0], y = cur[1], step = cur[2];
                for(int k = 0; k < 4; k++)
                {
                    int nx = x + dx[k], ny = y + dy[k];
                    if(nx < 0 || ny < 0 || nx >= h || ny >= w || grid[nx][ny] == '#') continue;
                    if(dp[nx][ny] <= step) continue;
                    dp[nx][ny] = step;
                    q.offer(new int[]{nx, ny, step});
                }
            }
            // System.out.println("....");
            while(!q2.isEmpty())
            {
                int[] cur = q2.poll();
                // System.out.println(Arrays.toString(cur));
                int x = cur[0], y = cur[1], step = cur[2];
                
                for(int xx = -2; xx <= 2; xx++)
                {
                    for(int yy = -2; yy <= 2; yy++)
                    {
                        int nx = x + xx, ny = y + yy;
                        if(nx < 0 || ny < 0 || nx >= h || ny >= w || grid[nx][ny] == '#') continue;
                        if(dp[nx][ny] <= step + 1) continue;
                        // System.out.printf("%d %d %d %d\n", nx, ny, dp[nx][ny], step + 1);
                        dp[nx][ny] = step + 1;
                        q.offer(new int[]{nx, ny, step + 1});
                    }
                }
            }
            
        }
        // for(int[] row : dp) System.out.println(Arrays.toString(row));
        if(dp[dh][dw] >= inf) out.println(-1);
        else out.println(dp[dh][dw]);
    }



    void c() throws Exception
    {
        int n = readInt();
        int[] ary = toIntArray();
        long sum = 0;
        int mini = 0;
        for(int i = 0; i < n; i++)
        {
            if(ary[i] < mini) sum += mini - ary[i];
            mini = Math.max(ary[i], mini);
        }
        out.println(sum);
        
    }

    int gcd(int a, int b)
    {
        if(b == 0) return a;
         return gcd(b, a % b);
    }

    void b() throws Exception
    {
        long[] ary = toLongArray();
        long a = ary[0], b = ary[1], c = ary[2], d = ary[3];
        long ac = a * c, ad = a * d, bc = b * c, bd = b * d;
        long ans = ac;
        ans = Math.max(ans, ad);
        ans = Math.max(ans, bc);
        ans = Math.max(ans, bd);
        out.println(ans);
    }

    boolean transform(String s1, String s2)
    {
        // from s1 -> s2
        int m = s1.length(), n = s2.length();
        if(m < n) return false;
        int j = n - 1;
        for(int i = m - 1; i >=0; i--)
        {
            if(s1.charAt(i) == s2.charAt(j)) j--;
            if(j < 0) return true;
        }
        return false;
    }

    void a() throws Exception
    {
        int x = readInt();
        out.println(1 - x);
        
    }
}

Measured memory_bytes: 33024