#include<fstream.h>
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,nr,i,j,a[2000000];
int main(){
	f>>n;
	for (i=2;i<=n;i++)
		a[i]=1;
	for (i=2;i<=n;i++)
		if(a[i]==1){
		for (j=2*i;j<=n;j=j+i)
			a[j]=0;
		nr++;
		}

g<<nr;
			return 0;
}