#include<fstream>
using namespace std;
char a[2000005];
long n,nr;
FILE *f=fopen("ciur.in","r"), *g=fopen("ciur.out","w");
int main()
{
	long j,i;
	fscanf(f,"%ld",&n);
	for(i=2;i<=n;i++) a[i]=1;
	for(i=2;i<=n;i++)
		if(a[i]!=0)
		{
			nr++;
			for(j=i+i;j<=n;j+=i)
				a[j]=0;
		}
	fprintf(g,"%ld",nr);
	return 0;
}