
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	}

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

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	} main {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		} int i = 0; int i = 0; i 0 i < K i K i++ i++ i {
			if(A > 0) {
				sum += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		} {
			if(A > 0) {
				sum += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		} if(A > 0) {
				sum += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			} A > 0 A 0 {
				sum += 1;
				A -= 1;
				continue;
			} sum += 1 sum 1 A -= 1 A 1 continue; if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			} B > 0 B 0 {
				sum += 0;
				B -= 1;
				continue;
			} sum += 0 sum 0 B -= 1 B 1 continue; {
				sum -= 1;
				C -= 1;
				continue;
			} sum -= 1 sum 1 C -= 1 C 1 continue; 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) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	}

} Main

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		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 += 1;
				A -= 1;
				continue;
			}else if(B > 0) {
				sum += 0;
				B -= 1;
				continue;
			} else {
				sum -= 1;
				C -= 1;
				continue;
			}
		}
		System.out.println(sum);
	}

}
