# include <cstdio>
# define N 2000010

using namespace std;

int sol,n;
bool prim[N];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d\n", &n);
    for(int i=2; i<=n; ++i)
        prim[i]=true;

    for(int i=2; i<=n; ++i)
        if(prim[i]==true)
        {
            sol++;
            for(int j=i; j<=n; j+=i)
                prim[j]=false;
        }
    printf("%d\n", sol);
}