#include <cstdio>
#include <iostream>
#include <bitset>
using namespace std;
bitset<1000000> prime;
unsigned long long N,i,j;

/*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,"%lld",&N);
	fclose(intrare);
	for(i=2;i<=N;i++)
	{
		j=2;
		if(prime[i]==0)
		{
			while(i*j<=N)
			{
				prime[i*j]=1;
				j++;
			}

		}
	}
	j=0;
	for(i=2;i<=N;i++) if(prime[i]==0) j++;
	iesire=fopen("ciur.out","w");
	fprintf(iesire,"%lld",j);
	fclose(iesire);

	return 0;
}