import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.FileInputStream;
import java.io.Writer;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author ilyakor
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream;
        try {
            inputStream = new FileInputStream("taxi.in");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        OutputStream outputStream;
        try {
            outputStream = new FileOutputStream("taxi.out");
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        taxi solver = new taxi();
        solver.solve(1, in, out);
        out.close();
    }
}

class taxi {
    public void solve(int testNumber, InputReader in, OutputWriter out) {
        long m = in.nextLong();
        long d = in.nextLong();
        int n = in.nextInt();
        long[] a = new long[n];
        int opti = -1;
        for (int i = 0; i < n; ++i) {
            a[i] = in.nextLong();
            if (a[i] >= m - d) {
                if (opti == -1 || a[i] < a[opti])
                    opti = i;
            }
        }
        if (opti == -1) {
            out.printLine(0);
            return;
        }
        long L = a[opti];
        a[opti] = -1;
        Arrays.sort(a);
        long pos = 0;
        int res = 0;
        for (int i = a.length - 1; i >= 0; --i) {
            if (L >= Math.abs(m - pos) + Math.abs(d - pos)) {
                ++res;
                pos = m;
                break;
            }
            long x = a[i];
            long d1 = Math.abs(d - pos);
            if (d1 > x) continue;
            x -= d1;
            ++res;
            pos += x;
            if (pos >= d) break;
        }
        if (pos < m) {
            long x = L;
            long d1 = Math.abs(d - pos);
            if (d1 <= x) {
                x -= d1;
                ++res;
                pos += x;
            }
        }
        if (pos < m) res = 0;
        out.printLine(res);
    }
}

class InputReader {
    private InputStream stream;
    private byte[] buffer = new byte[10000];
    private int cur;
    private int count;

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

    public static boolean isSpace(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    public int read() {
        if (count == -1) {
            throw new InputMismatchException();
        }
        try {
            if (cur >= count) {
                cur = 0;
                count = stream.read(buffer);
                if (count <= 0)
                    return -1;
            }
        } catch (IOException e) {
            throw new InputMismatchException();
        }
        return buffer[cur++];
    }

    public int readSkipSpace() {
        int c;
        do {
            c = read();
        } while (isSpace(c));
        return c;
    }

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

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

    }

class OutputWriter {
    private final PrintWriter writer;

    public OutputWriter(OutputStream outputStream) {
        writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public OutputWriter(Writer writer) {
        this.writer = new PrintWriter(writer);
    }

    public void print(Object... objects) {
        for (int i = 0; i < objects.length; i++) {
            if (i != 0) {
                writer.print(' ');
            }
            writer.print(objects[i]);
        }
    }

    public void printLine(Object... objects) {
        print(objects);
        writer.println();
    }

    public void close() {
        writer.close();
    }

    }