#include <iostream>
#include <cstdio>
using namespace std;

int n,nr;
char a[2000001];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for (int i=2;i<=n;i++)
        a[i]='1';
    for (int i=2;i<=n;i++)
        if (a[i]=='1')
        {
            nr++;
            for (int j=i+i;j<=n;j+=i)
                a[j]='0';
        }
    printf("%d",nr);
    return 0;
}