#include <fstream>
#include <cmath>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char a[2000000];
int nr=0,i,j,x,aa;
int main()
{   f>>x;
    for (int i=2;i<=x;i++)
        a[i]=1;
    for (i=2;i<=sqrt(x);i++)
        if (a[i]!=0)
        for (j=2;j<=x/i;j++)
            a[i*j] = 0;
    for(i=2;i<=x;i++)
    if (a[i]==1)
    aa++;
    g<<aa;
return 0;
}