#include <iostream>
#include <algorithm>


using namespace std;

bool prim(int n)
{
    for(int i=2; i*i<=n; i++)
        if(n%i==0)
            return 0;

    return 1;
}


int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n, cnt=0;
    cin>>n;
    for(int i=2; i<=n; i++)
        if(prim(i))
        cnt++;
    cout<<cnt;
    return 0;
}