#include <fstream>
#include <bitset>
using namespace std;
bitset <2000001>neprim;
int prim;
int main()
{
    int n;
    ifstream f1("ciur.in");
    ofstream f2("ciur.out");
    f1>>n;
    for (int y,i=2;i<=n;++i)
    {
        if (neprim[i])
            continue;
        ++prim;
        for (y=i+i;y<=n;y+=i)
            neprim[y]=1;
    }
    f2<<prim<<'\n';
    f1.close();
    f2.close();
    return 0;
}