#include <fstream.h>
#define N 2000001

ifstream fin("ciur.in");
ofstream fout("ciur.out");

char prim[N];
long n,nr;

void citire(){
     fin>>n;
}
void ciur(){
     long i,j;

     for(i=2;i<=n;++i)

	if(!prim[i]){
	  nr++;

	  for(j=i+i;j<=n;j+=i)
	     prim[j] = 1;
	}


     fout<<nr;
}

int main(){
    citire();
    ciur();
    return 0;
}