text: # Problem Julia is conducting an experiment in her lab.She placed several luminescent bacterial colonies in a horizontal testtube.Different types of bacteria can be distinguished by the color of light they emit.Julia marks types of bacteria with small Latin letters "a", ..., "z".The testtube is divided into n consecutive regions.Each region is occupied by a single colony of a certain bacteria type at any given moment.Hence, the population of the testtube at any moment can be described by a string of n Latin characters.Sometimes a colony can decide to conquer another colony in one of the adjacent regions.When that happens, the attacked colony is immediately eliminated and replaced by a colony of the same type as the attacking colony, while the attacking colony keeps its type.Note that a colony can only attack its neighbours within the boundaries of the testtube.At any moment, at most one attack can take place.For example, consider a testtube with population "babb".There are six options for an attack that may happen next: * the first colony attacks the second colony (1 → 2), the resulting population is "bbbb"; * 2 → 1, the result is "aabb"; * 2 → 3, the result is "baab"; * 3 → 2, the result is "bbbb" (note that the result is the same as the first option); * 3 → 4 or 4 → 3, the population does not change.The pattern of attacks is rather unpredictable.Julia is now wondering how many different configurations of bacteria in the testtube she can obtain after a sequence of attacks takes place (it is possible that no attacks will happen at all).Since this number can be large, find it modulo 109 + 7.Input The first line contains an integer n — the number of regions in the testtube (1 ≤ n ≤ 5 000).The second line contains n small Latin letters that describe the initial population of the testtube.Output Print one number — the answer to the problem modulo 109 + 7.