Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

ans = len(R)*len(G)*len(B)

m = min(B)
M = max(B)

for i in R:
    for j in G:
        a = 2*j - i 
        b = (i+j)//2 if (i+j)%2 == 0 else 0
        c = 2*i - j
        if m <= a <= M:
            if S[a-1] == "B":
                ans -= 1
        if b != 0 and S[b-1] == "B":
            ans -= 1
        if m <= c <= M:
            if S[c-1] == "B":
                ans -= 1
            
print(ans)
        


Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""
import sys

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

if R==[] or G==[] or B==[]:
    print(0)
    sys.exit()
    
ans = len(R)*len(G)*len(B)

m = min(B)
M = max(B)

for i in R:
    for j in G:
        a = 2*j - i 
        b = (i+j)//2 if (i+j)%2 == 0 else 0
        c = 2*i - j
        if m <= a <= M:
            if S[a-1] == "B":
                ans -= 1
        if b != 0 and S[b-1] == "B":
            ans -= 1
        if m <= c <= M:
            if S[c-1] == "B":
                ans -= 1
            
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

ans = len(R)*len(G)*len(B)
#print(R)
#print(G)
#print(B)

for i in R:
    for j in G:
        if 2*j - i in B:
            ans -= 1
        if (i+j)%2 == 0:
            if (i+j)//2 in B:
                ans -= 1
        if 2*i - j in B:
            ans -= 1

print(ans)
        


Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""
import sys

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

if R==[] or G==[] or B==[]:
    print(0)
    sys.exit()
    
ans = len(R)*len(G)*len(B)

m = min(B)
M = max(B)

for i in R:
    for j in G:
        a = 2*j - i 
        b = (i+j)//2 if (i+j)%2 == 0 else 0
        c = 2*i - j
        if m <= a <= M:
            if S[a-1] == "B":
                ans -= 1
        if b != 0 and S[b-1] == "B":
            ans -= 1
        if m <= c <= M:
            if S[c-1] == "B":
                ans -= 1
            
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

ans = len(R)*len(G)*len(B)
#print(R)
#print(G)
#print(B)

for i in R:
    for j in G:
        if 2*j - i in B:
            ans -= 1
        if (i+j)%2 == 0:
            if (i+j)//2 in B:
                ans -= 1
        if 2*i - j in B:
            ans -= 1

print(ans)
        


Fixed submission:
# -*- coding: utf-8 -*-
"""
Created on Wed May  6 02:13:01 2020

@author: shinba
"""
import sys

N = int(input())
S = input()

R = []
G = []
B = []

for i in range(N):
    if S[i] == "R":
        R.append(i+1)
    elif S[i] == "G":
        G.append(i+1)
    else:
        B.append(i+1)

if R==[] or G==[] or B==[]:
    print(0)
    sys.exit()
    
ans = len(R)*len(G)*len(B)

m = min(B)
M = max(B)

for i in R:
    for j in G:
        a = 2*j - i 
        b = (i+j)//2 if (i+j)%2 == 0 else 0
        c = 2*i - j
        if m <= a <= M:
            if S[a-1] == "B":
                ans -= 1
        if b != 0 and S[b-1] == "B":
            ans -= 1
        if m <= c <= M:
            if S[c-1] == "B":
                ans -= 1
            
print(ans)