#include <fstream>

using namespace std;

ifstream in ("ciur.in");
ofstream out ("ciur.out");

int main()
{
    int n,s=0;
    bool v[2000001]={0};
    v[0]=v[1]=1;
    in>>n;
    for(int i=2;i*i<=n;++i)
        if(v[i]==0)
            for(int j=i*i;j<=n;j+=i)
                v[j]=1;
    for(int i=2;i<=n;++i)
        if(v[i]==0)
            s++;
    out<<s;
    return 0;
}