#include <fstream>
#define MAXN 2000001
#define FIN "ciur.in"
#define FOUT "ciur.out"

using namespace std;
 
int sita[ MAXN ], N, count = 0;

//function prototypes
void eratosthenes();
void read();

int main() {

    read();
    eratosthenes(); 

    return(0);
};

void read() {

     ifstream f( FIN );

     f>>N; 

     f.close();
}

void eratosthenes() {

     int i,
         j;

     ofstream o( FOUT  );

     for(i = 2; i <= N; i++) sita[ i ] = 1; 
 
     for(i = 2; i <= N; i++) {

        if(sita[ i ]) {

           count++;

           for(j = i + i; j <= N; j += i) sita[ j ] = 0;
        }
     }
  
    o<<count;

    o.close();
};