#include <fstream>
using namespace std;
int n,cnt;
char prim[2000005];
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    int i,j;
    f>>n;
    for(i=2;i<=n;i++)
        prim[i]=1;
    for(i=2;i<=n;i++)
        if(prim[i]) {
            ++cnt;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
        g<<cnt;
    return 0;
}