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