#include<fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,v[2000001],k;
int main()
{
    f>>n;
    for(i=1;i<=n;++i)
        v[i]=1;
    for(i=2;i<=n;++i)
        if (v[i])
        for(j=2;j<=n;++j)
        v[i*j]=0;
    for(i=2;i<=n;++i)
        if(v[i]==1)
        k++;
    g<<k;
    g.close();
    return 0;
}