#include <cstdio>
#include <math.h>
using namespace std;
bool ciur[2000000];
int n;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    int pas = 2;
    int nr = 0;
    for(int pas = 2; pas <= n; pas++)
        {
            if(ciur[pas] == false)
            {
                nr++;
                for(int i = pas*2; i <= n; i+= pas)
                {

                    ciur[i] = true;


                }
            }


        }

    printf("%d",nr);


    return 0;
}