#include <fstream>

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