Each student eagerly awaits the day he would pass the exams successfully. Thus, Vasya was ready to celebrate, but, alas, he didn't pass it. However, many of Vasya's fellow students from the same group were more successful and celebrated after the exam.

Some of them celebrated in the BugDonalds restaurant, some of them — in the BeaverKing restaurant, the most successful ones were fast enough to celebrate in both of restaurants. Students which didn't pass the exam didn't celebrate in any of those restaurants and elected to stay home to prepare for their reexamination. However, this quickly bored Vasya and he started checking celebration photos on the Kilogramm. He found out that, in total, BugDonalds was visited by A students, BeaverKing — by B students and C students visited both restaurants. Vasya also knows that there are N students in his group.

Based on this info, Vasya wants to determine either if his data contradicts itself or, if it doesn't, how many students in his group didn't pass the exam. Can you help him so he won't waste his valuable preparation time?

Input

The first line contains four integers — A, B, C and N (0 ≤ A, B, C, N ≤ 100).

Output

If a distribution of N students exists in which A students visited BugDonalds, B — BeaverKing, C — both of the restaurants and at least one student is left home (it is known that Vasya didn't pass the exam and stayed at home), output one integer — amount of students (including Vasya) who did not pass the exam. 

If such a distribution does not exist and Vasya made a mistake while determining the numbers A, B, C or N (as in samples 2 and 3), output -1.

Examples

Input

10 10 5 20


Output

5

Input

2 2 0 4


Output

-1

Input

2 2 2 1


Output

-1

Note

The first sample describes following situation: 5 only visited BugDonalds, 5 students only visited BeaverKing, 5 visited both of them and 5 students (including Vasya) didn't pass the exam.

In the second sample 2 students only visited BugDonalds and 2 only visited BeaverKing, but that means all 4 students in group passed the exam which contradicts the fact that Vasya didn't pass meaning that this situation is impossible.

The third sample describes a situation where 2 students visited BugDonalds but the group has only 1 which makes it clearly impossible.
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;

public class Tester {

    public static void main(String[] args) {
        final int mod = (int) (1e9 + 7);
        final InputReader in = new InputReader(System.in);
        final PrintWriter out = new PrintWriter(System.out);

        final int a = in.nextInt();
        final int b = in.nextInt();
        final int c = in.nextInt();
        final int n = in.nextInt();

        final int left = n - a - b + c;
        if (left > 0 && c <= a && c <= b) {
            out.println(left);
        } else {
            out.println(-1);
        }

        out.close();
    }

    static long fac(long a) {
        long k = a;
        for (long i = 2; i < a; i++) {
            k = k * i;
        }
        System.out.println(k + " " + a);

        return a;

    }

    static class Pair implements Comparable<Pair> {

        int x, y;
        // int i;

        Pair(int x, int y) {
            this.x = x;
            this.y = y;
            // this.i = i;
        }

        @Override
        public int compareTo(Pair o) {
            if (this.x != o.x) {
                return Long.compare(this.x, o.x);
            } else {
                return Long.compare(this.y, o.y);
                // return 0;
            }
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof Pair) {
                final Pair p = (Pair) o;
                return p.x == x && p.y == y;// && p.i == i;
            }
            return false;
        }
    }

    public static boolean isPal(String s) {
        for (int i = 0, j = s.length() - 1; i <= j; i++, j--) {
            if (s.charAt(i) != s.charAt(j)) {
                return false;
            }
        }
        return true;
    }

    public static String rev(String s) {
        final StringBuilder sb = new StringBuilder(s);
        sb.reverse();
        return sb.toString();
    }

    public static long gcd(long x, long y) {
        if (x % y == 0) {
            return y;
        } else {
            return gcd(y, x % y);
        }
    }

    public static int gcd(int x, int y) {
        if (x % y == 0) {
            return y;
        } else {
            return gcd(y, x % y);
        }
    }

    public static long gcdExtended(long a, long b, long[] x) {

        if (a == 0) {
            x[0] = 0;
            x[1] = 1;
            return b;
        }
        final long[] y = new long[2];
        final long gcd = gcdExtended(b % a, a, y);

        x[0] = y[1] - (b / a) * y[0];
        x[1] = y[0];

        return gcd;
    }

    public static int abs(int a, int b) {
        return Math.abs(a - b);
    }

    public static long abs(long a, long b) {
        return Math.abs(a - b);
    }

    public static int max(int a, int b) {
        if (a > b) {
            return a;
        } else {
            return b;
        }
    }

    public static int min(int a, int b) {
        if (a > b) {
            return b;
        } else {
            return a;
        }
    }

    public static long max(long a, long b) {
        if (a > b) {
            return a;
        } else {
            return b;
        }
    }

    public static long min(long a, long b) {
        if (a > b) {
            return b;
        } else {
            return a;
        }
    }

    public static long pow(long n, long p, long m) {
        long result = 1;
        if (p == 0) {
            return 1;
        }
        if (p == 1) {
            return n;
        }
        while (p != 0) {
            if (p % 2 == 1) {
                result *= n;
            }
            if (result >= m) {
                result %= m;
            }
            p >>= 1;
            n *= n;
            if (n >= m) {
                n %= m;
            }
        }
        return result;
    }

    public static long pow(long n, long p) {
        long result = 1;
        if (p == 0) {
            return 1;
        }
        if (p == 1) {
            return n;
        }
        while (p != 0) {
            if (p % 2 == 1) {
                result *= n;
            }
            p >>= 1;
            n *= n;
        }
        return result;
    }

    static class InputReader {

        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private SpaceCharFilter filter;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int snext() {
            if (snumChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } catch (final IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0) {
                    return -1;
                }
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int n) {
            final int a[] = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextInt();
            }
            return a;
        }

        public long[] nextLongArray(int n) {
            final long a[] = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = nextLong();
            }
            return a;
        }

        public String readString() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            final StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = snext();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public String nextLine() {
            int c = snext();
            while (isSpaceChar(c)) {
                c = snext();
            }
            final StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = snext();
            } while (!isEndOfLine(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }
}