N=int(input())
S=list(input())
A=[]

for i in range(1,N+1):       
    A.append([])
    if i==1:
        for j in range(1,N+1):
            A[0].append([[j,S[j-1]]])
    else:
        for j in range(0,len(A[0])):
            for k in range(A[0][j][i-2][0]+1,N):    
                if A[0][j][i-2][1]!=S[k]:
                    A[1].append([])
                    for l in range(0,i):
                        A[1][len(A[1])-1].append(A[0][j][l])
                    A[1][len(A[1])-1].append([k,S[k]])
        A.remove(A[0])
    print(len(A[0]))