#include<stdio.h>
#include<cstring>
using namespace std;
FILE *f,*g;
int n,viz[2000002],nr;

void ciur()
{
	int i,j;
	for(i=2;i<=n;i++)
		if(viz[i]==0)
		{
			nr++;
			for(j=i+i;j<=n;j=j+i)
			viz[j]=1;
		}
}

int main()
{
	f=fopen("ciur.in","rt");
	fscanf(f,"%d",&n);
	fclose(f);
	ciur();
	g=fopen("ciur.out","wt");
	fprintf(g,"%d",nr);
	fclose(g);
	return 0;
}