#include <stdio.h>


#define nm 2000010

int n, i, j, sol;
char a[nm];

void read()

{
	scanf("%d ", &n);
}


void solve()

{
	sol = 0;
	for (i=2; i<=n; ++i)
	{
		if (a[i] == 0)
		{
			++sol;
			for (j=i+i; j<=n; j+=i)
			{
				a[j] = 1;
			}
		}
	}
}


void write()

{
	printf("%d\n", sol);
}


int main()

{
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out","w",stdout);

	read();
	solve();
	write();

	return 0;
}