#include <fstream>

using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
int N;
int E[200000001],nr;
int main()
{
    fi>>N;
    for (int i=2;i<=N;i++)
        E[i]=1;
    for (int i=2;i<=N;i++)
        if (E[i]==1)
            for (int j=i+i;j<=N;j=j+i)
                E[j]=0;
    for (int i=1;i<=N;i++)
        if (E[i]==1)
            nr++;
            fo<<nr;
    return 0;
}