A simple yet interesting problem in C#

Found this simple yet attractive problem..Just a matter of finding the right loop...

The objective is to find the total length of an object that goes through alternating cycles viz.cycle A and cycle B, doubling in length at the first instance and then increasing by 1 in the latter...The problem is to find the length after N iterations...

int tot = 1;

for (int u = 0; u < n; u++)
{

if ((u % 2) == 0) //cycle A
{
tot = tot * 2;
}
else //cycle B
{
tot += 1;
}
}

MessageBox.Show(tot.ToString());