Codeforces 1238 #Codeforces

1238D.py

def main():
    n = int(input())
    s = input()

    ret = n * (n - 1) // 2
    for x in range(2): # 正着来一遍，反着来一遍
        cur = 1
        for i in range(1, n):
            if s[i-1] == s[i]:
                cur += 1
            else:
                ret -= cur - x # AAB (rev)--> BAA 有重复计算
                cur = 1

        s = s[::-1]
    
    return ret

print(main())