#include <stdio.h>
#include <stdbool.h>
#define MAXN 2000001
#define FIN "ciur.in"
#define FOUT "ciur.out"

//global djs
bool sita[ MAXN ];
int n;

void erathostene();

int main() {

    int i, 
        count;

    freopen(FIN, "r", stdin);

    freopen(FOUT, "w", stdout);

    scanf("%d", &n);  

    erathostene();

    count = 0;

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

        if(sita[ i ] == true) count++; 

    printf("%d", count);

    return(0);
};

void erathostene() {

     int i, 
         j; 

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

         sita[ i ] = true; 
     }

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

        j = 2;

        while( i * j <= n ) {

              sita[i*j] = false;

              j++;
        }
    }     

}