include [HTML_REMOVED]

include [HTML_REMOVED]

include [HTML_REMOVED]

using namespace std;
bool check(int x)
{

int count=1;
while (x)
{
    //int r=x%10;
    if(x%2!=count%2) return false;
    x/=10; count++;
}
return true;

}
int main()
{
int n;
cin >> n;
int res=0;
for (int i = 1; i <=n; i )
{
if(check(i))
{
res;
}

}
cout << res<<endl;
return 0;

}