#include <stdio.h>

int main() {
    char v[2000001];
    int n,cate = 0,i,j;
    
    FILE *f = fopen("ciur.in","r");
    freopen("ciur.out","w",stdout);
    
    fscanf(f,"%i",&n);
    fclose(f);
    
    for (i=2; i <= n; i++) {
        v[i] = '1';
    }
    
    for (i=2; i <= n; i++) {
         if (v[i] = '1') {
               ++cate;
               for (j=i+i; j <= n; j+=i) {
                   v[i] = '0';
               }
         }      
    }                  
    
    printf("%i",cate);
       
    return 0;
}