import java.util.Scanner;

public class Main {

    public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    }
}

class B {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        final int res = calc(n, d);
        System.out.println(res);
    }
    static int calc(final int n, final int d) {
        final int max = (2 * d + 1);
        int res = n / max;
        if (n % max != 0) {
            res += 1;
        }
        return res;
    }
}

class A {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int r = sc.nextInt();
        final int res = calc(r);
        System.out.println(res);
    }

    static int calc(final int r) {
        return 3 * r * r;
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    }
} Main public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    } main {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    } final String mode = "b"; mode "b" if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        } mode.equals("a") mode.equals mode "a" {
            A.solve();
        } A.solve() A.solve A if (mode.equals("b")) {
            B.solve();
        } mode.equals("b") mode.equals mode "b" {
            B.solve();
        } B.solve() B.solve B final String... args args class B {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        final int res = calc(n, d);
        System.out.println(res);
    }
    static int calc(final int n, final int d) {
        final int max = (2 * d + 1);
        int res = n / max;
        if (n % max != 0) {
            res += 1;
        }
        return res;
    }
} B static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        final int res = calc(n, d);
        System.out.println(res);
    } solve {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        final int res = calc(n, d);
        System.out.println(res);
    } final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc final int d = sc.nextInt(); d sc.nextInt() sc.nextInt sc final int res = calc(n, d); res calc(n, d) calc n d System.out.println(res) System.out.println System.out System System.out res static int calc(final int n, final int d) {
        final int max = (2 * d + 1);
        int res = n / max;
        if (n % max != 0) {
            res += 1;
        }
        return res;
    } calc {
        final int max = (2 * d + 1);
        int res = n / max;
        if (n % max != 0) {
            res += 1;
        }
        return res;
    } final int max = (2 * d + 1); max (2 * d + 1) 2 * d 2 d 1 int res = n / max; res n / max n max if (n % max != 0) {
            res += 1;
        } n % max != 0 n % max n max 0 {
            res += 1;
        } res += 1 res 1 return res; res final int n n final int d d class A {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int r = sc.nextInt();
        final int res = calc(r);
        System.out.println(res);
    }

    static int calc(final int r) {
        return 3 * r * r;
    }
} A static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int r = sc.nextInt();
        final int res = calc(r);
        System.out.println(res);
    } solve {
        final Scanner sc = new Scanner(System.in);
        final int r = sc.nextInt();
        final int res = calc(r);
        System.out.println(res);
    } final Scanner sc = new Scanner(System.in); sc new Scanner(System.in) final int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc final int res = calc(r); res calc(r) calc r System.out.println(res) System.out.println System.out System System.out res static int calc(final int r) {
        return 3 * r * r;
    } calc {
        return 3 * r * r;
    } return 3 * r * r; 3 * r * r 3 * r * r 3 r r final int r r public class Main {

    public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    }
} public class Main {

    public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(final String... args) {
        final String mode = "b";

        if (mode.equals("a")) {
            A.solve();
        } else if (mode.equals("b")) {
            B.solve();
        }
    }
}

class B {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int n = sc.nextInt();
        final int d = sc.nextInt();
        final int res = calc(n, d);
        System.out.println(res);
    }
    static int calc(final int n, final int d) {
        final int max = (2 * d + 1);
        int res = n / max;
        if (n % max != 0) {
            res += 1;
        }
        return res;
    }
}

class A {
    static void solve() {
        final Scanner sc = new Scanner(System.in);
        final int r = sc.nextInt();
        final int res = calc(r);
        System.out.println(res);
    }

    static int calc(final int r) {
        return 3 * r * r;
    }
}