n=int(input())
s=[ord(c)-ord("A") for c in input()]
k=26
cc=[[0]*(n+1) for i in range(k)]
for i in reversed(range(n)):
  cc[s[i]][i]=1
  for j in range(k):
    cc[j][i]+=cc[j][i+1]
a=0
q=[[0]*(k+1) for i in range(k)]
for i in range(n):
  c=s[i]
  for j in range(k):
    if j!=c:
      ccc=(n-1-i)-cc[c][i+1]-cc[j][i+1]
      a+=q[c][j]*ccc*(ccc-1)//2
  for j in range(k):
    if j!=c:
      q[j][c]+=q[j][k]
  q[c][k]+=1
print(a)