#include <fstream>
using namespace std;
ifstream in("nrbin.in");
ofstream out("nrbin.out");
int baza2(int n)
{
    int nr=0,p=1;
    while(n)
    {
        nr=nr+(n%2)*p;
        p=p*10;
        n=n/2;
    }
    return nr;
}
int main()
{
    int n,i;
    in>>n;
    for( i=1; baza2(i)<=n; i++)
    {

    }
    out<<i-1;
// out<<" "<<baza2(i-1);
    return 0;
}