/* 
 * File:   main.c
 * Author: Dani
 *
 * Created on 03 martie 2013, 17:34
 */

#include <stdio.h>
#include <stdlib.h>

/*
 * 
 */

char prim[2000000];

int main() {
    FILE *fin, *fout;
    int n, c = 0;
    int i, j;
    
    fin = fopen("ciur.in","r");
    fscanf(fin,"%d", &n);
    fclose(fin);
  
    for (i = 2; i <= n; i++)
    {
        if(prim[i] == 0) {
            c++;
            for(j = i + i; j <= n; j+=i)
                prim[j] = 1;
        }
    }
    
    fout = fopen("ciur.out","w");
    fprintf(fout,"%d",c);
    fclose(fout);
    
    return 0;
}