Problem:
Score : 400 points

Problem Statement

We have a string S of length N consisting of R, G, and B.

Find the number of triples (i,~j,~k)~(1 \leq i < j < k \leq N) that satisfy both of the following conditions:

S_i \neq S_j, S_i \neq S_k, and S_j \neq S_k.

j - i \neq k - j.

Constraints

1 \leq N \leq 4000

S is a string of length N consisting of R, G, and B.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of triplets in question.

Sample Input 1

4
RRGB

Sample Output 1

1

Only the triplet (1,~3,~4) satisfies both conditions. The triplet (2,~3,~4) satisfies the first condition but not the second, so it does not count.

Sample Input 2

39
RBRBGRBGGBBRRGBBRRRBGGBRBGBRBGBRBBBGBBB

Sample Output 2

1800

Solution in Pascal (FPC 3.0.4) (judge verdict: Time Limit Exceeded)

var s:ansistring;
i,j,k,ans,n:longint;
begin
  readln(n);
  readln(s);
  for i:=1 to n do
    for j:=i to n do
      for k:=j to n do
        if (s[i]<>s[j]) and (s[k]<>s[j]) and (s[i]<>s[k]) and (j-i<>k-j) then
          inc(ans);
  writeln(ans);
end.