#include<stdio.h>
int N,v[2000000],cont=0;
void marcare(int a)
{ int b=2*a;
	for(b;b<N;b=b+a){
		v[b]=0;
	}
}

int main()
{	
	FILE*fin=fopen("ciur.in","r");
	FILE*fout=fopen("ciur.out","w");
	fscanf(fin,"%d",&N);
	for(int i=2;i<N;i++)
	{ v[i]=1;}
	for(int i=2;i<N;i++)
	{
		if(v[i]==1)
	{
		cont++;
		marcare(i);
	}
}
fprintf(fout,"%d",cont);
fclose(fin);
fclose(fout);
return 0;
}