#include <fstream>

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