#include <fstream>
using namespace std;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,nr=0;
    bool *v;
    f>>n;
    v=new bool[n];
    v[0]=false;
    for(int i=1;i<n;++i)
        v[i]=true;
    for(int i=2;i*i<=n;++i)
        if(v[i-1])
            for(int j=i*i;j<=n;j+=i)
                v[j-1]=false;
    for(unsigned long long i=0;i<n;++i)
        if(v[i])
            ++nr;
    g<<nr;
    delete v;
    return 0;
}