#include <stdio.h>

char marc[2000000];
long nprime,i,k,n;

int main(){
    
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    scanf("%ld",&n);
    for(i=2;i<=n;i++) marc[i]='0';
    for(i=2;i<=n;i++)
          if (marc[i]=='0'){ k=2; while (i*k<=n) marc[i*(k++)]='1';}

    for(i=2;i<=n;i++)    if (marc[i]=='0') nprime++;
    
    printf("%ld",nprime);

    return 0;
    
}