#include<stdio.h>
#define M 2000001
FILE *f=fopen("ciur,in","r");
FILE *g=fopen("ciur.out","w");

char ciur[M];

void ciurr(long n)
{
	long i,j;
	
	for(i=2;i<=n;i++)
		ciur[i]=1;
	
	for(i=2;i<=n;i++)
		if(ciur[i]) for(j=2;j<=n/i;j++)
			           ciur[i*j]=0;
}

int main()
{
	long i,n,k=0;
	
	fscanf(f,"%ld",&n);
	
	ciurr(n);
	
	for(i=2;i<=n;i++)
		if(ciur[i]) k++;
	
	fprintf(g,"%ld\n",k);
	fclose(f);
	fclose(g);
	return 0;
}