#include <cstdio> 
using namespace std;
int n,i,nr,j;
int main () { 
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%lld",&n);
	int v[2000010];
	
	for ( i = 2 ; i <= n ; ++i ) 
		v[i] = 1;
	for ( i = 2 ; i <= n ; ++i )
	{
		if( v[i] )
		{
			nr++;
			for( j = i+i; j <= n ; j+=i )
				v[j] = 0;
		}
	}
	printf("%lld",nr);
}