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
i,j,k,N:Longint;
S:String;
R,G,B,ans:int64;
begin
readln(N);
readln(S);
for i:=1 to N do if S[i]='R'then inc(R)else if S[i]='B'then inc(B)else inc(G);
ans:=R*G*B;
for i:=1 to N do for j:=i+2 to N do if(j-i)mod 2=0 then begin
if(S[i]<>S[j])and(S[i]<>S[(i+j)div 2])and(S[j]<>S[(i+j)div 2])then dec(ans);
end;
writeln(ans);
end.