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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    }
} 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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    }
} 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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    } main {
    Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        int C = sc.nextInt();
        int K = sc.nextInt();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    } 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 int sum = 0; sum 0 for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    } int i=0; int i=0; i 0 i<K i K i++ i++ i {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    } {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    } if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      } A>0 A 0 {
        sum++;
        A--;
      } sum++ sum A-- A if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      } B>0 B 0 {
        B--;
      } B-- B if(C>0) {
        sum--;
        C--;
      } C>0 C 0 {
        sum--;
        C--;
      } sum-- sum C-- C System.out.println(sum) System.out.println System.out System System.out sum 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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    }
} 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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    }
} 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();
        int sum = 0;
    
    for(int i=0; i<K; i++) {
      if(A>0) {
        sum++;
        A--;
      } else if(B>0) {
        B--;
      } else if(C>0) {
        sum--;
        C--;
      }
    }
    System.out.println(sum);
    }
}