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

bool v[2000001];

int main()
{
    int n,d,i,cont=0;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    fclose(stdin);
    for(d=2;d<n;d++){
        if(v[d]==false){
            cont++;
            for(i=d*d;i<=n;i+=d)
                v[i]=true;
        }
    }
    printf("%d",cont);
    return 0;
}