Subcontests
(4)among d_1=x_2-x_1, d_2=x_3-x_2, ..., d_{101}=x_{102}-x_{101}, 26 are equal
Let x1,x2,x3,...,x102 be natural numbers such that x1<x2<x3<...<x102<255.
Prove that among the numbers d1=x2−x1,d2=x3−x2,...,d101=x102−x101 there are at least 26 equal.