import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    }
} Main public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) Task solver = new Task(); solver new Task() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    } Task public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        } solve {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        } int A = in.nextInt(); A in.nextInt() in.nextInt in int B = in.nextInt(); B in.nextInt() in.nextInt in int C = in.nextInt(); C in.nextInt() in.nextInt in int K = in.nextInt(); K in.nextInt() in.nextInt in int sum = 0; sum 0 while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            } A > 0 && K > 0 A > 0 A 0 K > 0 K 0 {
                sum += 1;
                A--;
                K--;
            } sum += 1 sum 1 A-- A K-- K while (B > 0 && K > 0)
            {
                B--;
                K--;
            } B > 0 && K > 0 B > 0 B 0 K > 0 K 0 {
                B--;
                K--;
            } B-- B K-- K while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            } C > 0 && K > 0 C > 0 C 0 K > 0 K 0 {
                sum -= 1;
                C--;
                K--;
            } sum -= 1 sum 1 C-- C K-- K out.println(sum) out.println out sum int testNumber testNumber Scanner in in PrintWriter out out public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    }
} public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1, in, out);
        out.close();
    }

    static class Task
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int A = in.nextInt();
            int B = in.nextInt();
            int C = in.nextInt();
            int K = in.nextInt();

            int sum = 0;

            while (A > 0 && K > 0)
            {
                sum += 1;
                A--;
                K--;
            }
            while (B > 0 && K > 0)
            {
                B--;
                K--;
            }
            while (C > 0 && K > 0)
            {
                sum -= 1;
                C--;
                K--;
            }
            out.println(sum);
        }

    }
}

