import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.io.PrintStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.Iterator; public class Main_yukicoder123 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); Printer pr = new Printer(System.out); int n = sc.nextInt(); int m = sc.nextInt(); int[] a = new int[m]; for (int i = 0; i < m; i++) { a[i] = sc.nextInt(); } int p = 1; for (int i = m - 1; i >= 0; i--) { if (p == 1) { p = a[i]; } else if (p <= a[i]) { p--; } } pr.println(p); pr.close(); sc.close(); } @SuppressWarnings("unused") private static class Scanner { BufferedReader br; Iterator it; Scanner (InputStream in) { br = new BufferedReader(new InputStreamReader(in)); } String next() throws RuntimeException { try { if (it == null || !it.hasNext()) { it = Arrays.asList(br.readLine().split(" ")).iterator(); } return it.next(); } catch (IOException e) { throw new IllegalStateException(); } } int nextInt() throws RuntimeException { return Integer.parseInt(next()); } long nextLong() throws RuntimeException { return Long.parseLong(next()); } float nextFloat() throws RuntimeException { return Float.parseFloat(next()); } double nextDouble() throws RuntimeException { return Double.parseDouble(next()); } void close() { try { br.close(); } catch (IOException e) { // throw new IllegalStateException(); } } } private static class Printer extends PrintWriter { Printer(PrintStream out) { super(out); } } }