#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int prim[2000005];
int main()
{   int n, i, j, cont=0;
    f>>n;
    for (i=2;i<=n;++i)
        prim[i]=1;
    for (i=2;i<=n;++i)
        if (prim[i]!=0)
        {   ++cont;
            for (j=i+i;j<=n;j=j+i)
                prim[j]=0;
        }
    g<<cont;
    return 0;
}