#include <stdio.h>
#define MAXN 2000001
#define FIN "ciur.in"
#define FOUT "ciur.out"
 
int sita[ MAXN ], N, count = 0;

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

int main() {

    read();
    eratosthenes(); 

    return(0);
};

void read() {

     freopen(FIN, "r", stdin);

     scanf("%d", &N);

     fclose( stdin );     
}

void eratosthenes() {

     int i,
         j;

     freopen(FOUT, "w", stdout);

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

        if(sita[ i ]) {

           count++;

           j = i + i;
   
           while( j <= N ) {

               sita[ j ] = 0; 

               j += i;
           } 
        }
     }
  
     printf("%d", count);

     fclose( stdout );     
};