#include <iostream>
#include <stdio.h>
using namespace std;

int p[2000001];
int main()
{
    int n,nr=0;

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

    scanf("%d",&n);
    for (int i=2;i<=n;i++) p[i]=1;
    for (int i=2;i<=n;i++)
        if (p[i]!=0)
        {
            nr++;
            for (int j=i;j<=n;j+=i) p[j]=0;
        }
    printf("%d\n", nr);

    return 0;
}