#include <bits/stdc++.h>
using namespace std;

int x[5000010];

int main()
{
	int n, maxn = 0;
	cin >> n;

	for (int i = 2; i * i <= n; i++)
		if (x[i] == 0)
			for (int j = 2; i * j <= n; j++)
				x[i * j] = 1;

	for (int i = 2; i <= n; )
	{
		if (x[i] == 1)
		{
			int cnt = 0;
			while (x[i] == 1 )
			{
				cnt++;
				i++;
			}
			if (cnt > maxn)
				maxn = cnt;
		}
		else
			i++;

	}
	cout << maxn << endl;
	return 0;
}