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: Accepted)

var n,i,j,r,g,b,cnt  :int64;
    s:string;

begin
  readln(n);
  readln(s);
  r:=0; g:=0; b:=0; cnt:=0;
  for i:=1 to n do begin
    if s[i]='R' then inc(r,1);
    if s[i]='G' then inc(g,1);
    if s[i]='B' then inc(b,1);
  end;
  for i:=1 to n-1 do
    for j:=i to n do begin
      if ((j-i)mod 2=0)and(s[i]<>s[j])and(s[j]<>s[(i+j)div 2])and(s[i]<>s[(i+j)div 2])
      then inc(cnt,1)
    end;
  writeln(r*g*b-cnt)
end.