    import java.util.Scanner;
     
     
    public class Main {
        

        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        }
    } import java.util.Scanner; Scanner java.util public class Main {
        

        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        }
    } Main public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        } main {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc int b = sc.nextInt(); b sc.nextInt() sc.nextInt sc int c = sc.nextInt(); c sc.nextInt() sc.nextInt sc int k = sc.nextInt(); k sc.nextInt() sc.nextInt sc if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        } a >= k a k {
            System.out.println(k);
        } System.out.println(k) System.out.println System.out System System.out k if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        } a + b >= k a + b a b k {
            System.out.println(a);
        } System.out.println(a) System.out.println System.out System System.out a if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        } a + b + c >= k a + b + c a + b + c a b c k {
            System.out.println(a - (c - ((a + b + c) - k)));
        } System.out.println(a - (c - ((a + b + c) - k))) System.out.println System.out System System.out a - (c - ((a + b + c) - k)) a (c - ((a + b + c) - k)) c ((a + b + c) - k) (a + b + c) a + b + c a b c k String[] args args public class Main {
        

        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        }
    } public class Main {
        

        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        }
    } Main
    import java.util.Scanner;
     
     
    public class Main {
        

        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            int k = sc.nextInt();
 
                    if (a >= k) {
            System.out.println(k);
        } else if (a + b >= k) {
            System.out.println(a);
        } else if (a + b + c >= k) {
            System.out.println(a - (c - ((a + b + c) - k)));
        }

            
            
        }
    }