#include <fstream>

using namespace std;

bool p[2000003];

int main()
{
    int i,j,x,n;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    x=0;
    p[2]=1;
    for(i=4;i<=n;i+=2) p[i]=1;
    for(i=3;i*i<=n;i+=2)
        if (p[i]==0) for (j=i*i;j<=n;j=j+2*i) p[j]=1;
    for(i=1;i<=n;i++) if(p[i]==0) x++;
    fout<<x<<"\n";
    fin.close();
    fout.close();
    return 0;
}