#include <stdio.h>

int main()
{
	int i,j,n,nr=0;
	bool c[2000000]={false};
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for (i=2;i*i<=n;++i)
		if (!c[i])
			for (j=i*i;j<=n;j+=i)
				c[j]=true;
	for (i=2;i<=n;++i)
		if (!c[i]) 
			++nr;
	printf("%d",nr);
	return 0;
}