#include <fstream>

using namespace std;

char s[2000000];
int counter;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n;
    f>>n;
    int i,j;
    for (i=2;i<=n;++i)
        s[i]=1;
    for (i=2;i<=n;++i)
    {
        if(s[i])
        {
            counter++;
            for (j=i+i;j<=n;j+=i)
                s[j]=0;
        }
    }
    g<<counter;
    return 0;
}