In this winter holiday, Bob has a plan for skiing at the mountain resort. This ski resort has MM different ski paths and NN different flags situated at those turning points. The ii-th path from the
The numbers 11, 33, 66, 1010, 1515, 2121, 2828, 3636, 4545 and t_i=\frac{1}{2}i(i+1)ti=21i(i+1), are called half-consecutive. For given NN, find the smallest rr which is no smaller than NN