#include<fstream>
#include<cstdio>

using namespace std;

const int MaxN = 2000001;

const char InFile[] = "ciur.in";
const char OutFile[] = "ciur.out";

int n,cnt;
bool prim[MaxN];

int main()
{
	freopen( InFile , "r" , stdin );
	freopen( OutFile , "w" , stdout );
	scanf("%d" , &n );
	int i,j;
	cnt = 0;
	for( i = 2 ; i <= n ; i++ )
		if( !prim[i] )
			{
				++cnt;
				for( j = i<<1 ; j <= n ; j += i )
					prim[j] = 1;
			}
	printf("%d\n" , cnt);
	return 0;
}