#include <cstdio>

using namespace std;

int n;
bool ciur[2000005];

inline void Ciur()
{
	int i,j,sol=1;
	for(i=3;i*i<=n;i+=2)
		if(ciur[i]==false)
			for(j=i*i;j<=n;j+=2*i)
				ciur[j]=true;
	for(i=3;i<=n;i+=2)
		if(ciur[i]==false)
			sol++;
	printf("%d\n", sol);
}

int main()
{
	freopen ("ciur.in","r",stdin);
	freopen ("ciur.out","w",stdout);
	scanf("%d", &n);
	Ciur();
	return 0;
}