#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,i,b,j,prime;
bitset <2000050> f;
int main()
{
    in>>n;
    f[1]=1;
    f[0]=1;
    for (i=2;i*i<=n;++i)
    {
        if (!f[i])
        {
            b=n/i;
            for (j=i;j<=b;++j)
                 f[i*j]=1;
        }
    }
    for (i=2;i<=n;++i)
    {
        if (!f[i]) prime++;
    }
    out<<prime<<"\n";
}