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

int n,nrprime;
char prim[2000005];


void citire()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
}


void ciur()
{
    nrprime=0;


    int i,j;

    for (i=2; i<=n; i++)
    {
        if (prim[i]==0)
        {
            nrprime++;
            for (j=i; j<=n; j=j+i)
                {
                    prim[j]=1;
                }
        }
    }
}


int main()
{
    citire();
    ciur();
    printf("%d",nrprime);
    return 0;
}