#include <cstdio>
#include <iostream>
#include <bitset>
using namespace std;
bitset<2000000> prime;
int N,i,j,contor;

/*int pcheck(long long k)
{ 	
	prime[0]=0;
 	long long p;
	for(p=2;p<=k/2;p++) 
	{if(p%k==0) {prime[0]=1; break;}}
	return prime[0];
}
*/
int main()
{
	FILE *intrare,*iesire;
	intrare=fopen("ciur.in","r");
	fscanf(intrare,"%d",&N);
	fclose(intrare);
	contor=0;
	for(i=2;i<=N;i++)
	{
		if(prime[i]==0)
		{
			for(j=i+i; j<=N; j=i+j) { prime[j]=1;} 
			contor++;
		}
	}
	iesire=fopen("ciur.out","w");
	fprintf(iesire,"%d",contor);
	fclose(iesire);

	return 0;
}