#include<cstdio>
const int N=2000001;
bool c[N];

int main()
{
	int n;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(int j=4; j<=n; j+=2)
		c[j]=true;
	for (int i=3; i*i<=n; i+=2)
		if (!c[i])
			for (int j=i*i; j<=n; j+=i)
				c[j]=true;
	int nr=0;
	for (int i=2; i<=n; ++i)
		if (!c[i])
			++nr;
	printf("%d",nr);
	return 0;
}