import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {
    public static void main(String[] args) throws IOException {

        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        List<Integer> integers = new ArrayList<>();
        List<Integer> lengths = new ArrayList<>();

        while (true) {
            String sN = reader.readLine();
            int n = Integer.parseInt(sN);
            if (n >= 10000) {
                return;
            }
            integers.add(n);
            if (integers.size() >= 1000) {
                return;
            }
            if (n == 0) {
                break;
            }
        }

        int n = 1;

        for (int i = 1; i < integers.size(); i++) {
            if (integers.get(i).equals(integers.get(i - 1) + 1)) {
                n++;
                if (i == integers.get(integers.size() - 1)) {
                    lengths.add(n);
                }
            } else {
                lengths.add(n);
                n = 1;
            }
        }

        Collections.reverse(integers);
        n = 1;

        for (int i = 1; i < integers.size(); i++) {
            if (integers.get(i).equals(integers.get(i - 1) + 1)) {
                n++;
                if (i == integers.get(integers.size() - 1)) {
                    lengths.add(n);
                }
            } else {
                lengths.add(n);
                n = 1;
            }
        }

        lengths.sort((o1, o2) -> o2 - o1);
        System.out.println(lengths.get(0));
    }
}