#include<cstdio>
#define N 2000001
bool c[N];
int n;
int ciur(int n)
{
	int i,j,nr=0;
	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++;
	return nr;
}
			
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	printf("%d\n",ciur(n));
	return 0;
}