#include<fstream>
#include<bitset>
#define maxn 2000005

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bitset <maxn> a;

long long n,i,j,p;

int main()
{
    f>>n;

    for(i=4;i<=n;i+=2)
        a[i]=1;

    p=1;

    for(i=3;i<=n;i+=2)
        if(!a[i])
        {
            ++p;
            for(j=i*i;j<=n;j+=i)
                a[j]=1;
        }

    g<<p<<"\n";

    f.close();
    g.close();

    return 0;
}