#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main(void){
	 int i , cnt=0 , j , N ;
	 char prim[2000005];
	 fin>>N;
	 for (i = 2; i <= N; ++i)
     prim[i] = 1;
     for (i = 2; i <= N; ++i)
     if (prim[i]){
     ++cnt;
     for (j = i+i; j <= N; j += i)
     prim[j] = 0;
     }
	 fout<<cnt;
return 0 ;
}