#include <fstream>

using namespace std;
bool v[2000000];
int main()
{
    long i,j,n,c=0;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (i=2;i*i<=n;i++)
        if(!v[i])
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
    for (i=2;i<=n;i++)
        if (v[i]==0)
            c++;
    g<<c;
    return 0;
}