#include <fstream>
using namespace std;
char prim[1000001];
int ct,n;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for(int i=2;i<=n;++i)//acesta este ciurul lui Eratostene
        if(!prim[i])
        {
            ++ct;
            for(int j=2*i;j<=n;j+=i)
                prim[j]=1;
        }
    printf("%d\n", ct);
    return 0;
}