//
#include<stdio.h>
FILE *f=fopen("ciur.in","r"), *g=fopen("ciur.out","w");
bool v[2000001];
long k,i,j,pozp,p,n,ctr;

int main()
{
	fscanf(f,"%ld", &n);
	
	
	for(i=2;i<=n;i++)
		v[i]=1;
	
	
	for(i=2;i<=n;i++)
		if(v[i])
		{
			++k;
			for(j=2*i;j<=n;j=j+i)
				v[j]=0;
			
		}
		
	

	fprintf(g,"%ld",k);
	
	fclose(f);
	fclose(g);
	return 0;
	
}