#include <stdio.h>
int nr;
void ciur(int n)
{
	int i,j;
	char p[2000005]={0};
	for (i=2;i<=n;i++)
	{
		if (!p[i])
		{
			for (j=i;j<=n;j+=i)
				p[j]=1;
			nr++;
		}
	}
}
int main()
{
	FILE *in,*out;
	int n;
	in=fopen("ciur.in","r");
	out=fopen("ciur.out","w");
	fscanf(in,"%d",&n);
	ciur(n);
	fprintf(out,"%d\n",nr);
	fclose(in);
	fclose(out);
	return  0;
	
}