Buggy python submission (verdict: Time Limit Exceeded):
import collections
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))

#j-i=k-jではない 2j=k+i i=2j-k

s = input()
count = 0

"""
for i in range(n):
    for j in range(i+1, n):
        if s[i]!=s[j]:    
            for k in range(j+1, n):
                if j-i!=k-j:
                    if s[i]!=s[k] and s[j]!=s[k]:
                        count += 1
"""
for i in range(n):
    a = s[i:]
    if s[i]=="R":
        point = a.count("G")*a.count("B")
    elif s[i]=="G":
        point = a.count("R")*a.count("B")
    else:
        point = a.count("R")*a.count("G")
    count += point

#j-i=k-jではない 2j=k+i i=2j-k
#rgb

kom = 0
for i in range(n):
    for j in range(i+1, n):
        if 2*j-i < n:
            if s[i]!=s[j] and s[i]!=s[2*j-i] and s[j]!=s[2*j-i]:
                kom += 1


print(count-kom)





Fixed submission:
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))

#j-i=k-jではない 2j=k+i i=2j-k

s = input()
count = 0

"""
for i in range(n):
    for j in range(i+1, n):
        if s[i]!=s[j]:    
            for k in range(j+1, n):
                if j-i!=k-j:
                    if s[i]!=s[k] and s[j]!=s[k]:
                        count += 1
"""
for i in range(n):
    a = s[i:]
    if s[i]=="R":
        point = a.count("G")*a.count("B")
    elif s[i]=="G":
        point = a.count("R")*a.count("B")
    else:
        point = a.count("R")*a.count("G")
    count += point

#j-i=k-jではない 2j=k+i i=2j-k
#rgb

kom = 0
for i in range(n):
    for j in range(i+1, n):
        if 2*j-i < n:
            if s[i]!=s[j] and s[i]!=s[2*j-i] and s[j]!=s[2*j-i]:
                kom += 1


print(count-kom)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))


s = input()
count = 0
for i in range(n):
    for j in range(i+1, n):
        if s[i]!=s[j]:    
            for k in range(j+1, n):
                if j-i!=k-j:
                    if s[i]!=s[k] and s[j]!=s[k]:
                        count += 1

print(count)





Fixed submission:
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))

#j-i=k-jではない 2j=k+i i=2j-k

s = input()
count = 0

"""
for i in range(n):
    for j in range(i+1, n):
        if s[i]!=s[j]:    
            for k in range(j+1, n):
                if j-i!=k-j:
                    if s[i]!=s[k] and s[j]!=s[k]:
                        count += 1
"""
for i in range(n):
    a = s[i:]
    if s[i]=="R":
        point = a.count("G")*a.count("B")
    elif s[i]=="G":
        point = a.count("R")*a.count("B")
    else:
        point = a.count("R")*a.count("G")
    count += point

#j-i=k-jではない 2j=k+i i=2j-k
#rgb

kom = 0
for i in range(n):
    for j in range(i+1, n):
        if 2*j-i < n:
            if s[i]!=s[j] and s[i]!=s[2*j-i] and s[j]!=s[2*j-i]:
                kom += 1


print(count-kom)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))


s = input()
count = 0
for i in range(n):
    for j in range(i+1, n):
        for k in range(j+1, n):
            if j-i!=k-j:
                if s[i]!=s[j] and s[i]!=s[k] and s[j]!=s[k]:
                    count += 1
print(count)





Fixed submission:
n = int(input())
#h  = list(map(int, input().split()))
#h, w = list(map(int, input().split()))

#j-i=k-jではない 2j=k+i i=2j-k

s = input()
count = 0

"""
for i in range(n):
    for j in range(i+1, n):
        if s[i]!=s[j]:    
            for k in range(j+1, n):
                if j-i!=k-j:
                    if s[i]!=s[k] and s[j]!=s[k]:
                        count += 1
"""
for i in range(n):
    a = s[i:]
    if s[i]=="R":
        point = a.count("G")*a.count("B")
    elif s[i]=="G":
        point = a.count("R")*a.count("B")
    else:
        point = a.count("R")*a.count("G")
    count += point

#j-i=k-jではない 2j=k+i i=2j-k
#rgb

kom = 0
for i in range(n):
    for j in range(i+1, n):
        if 2*j-i < n:
            if s[i]!=s[j] and s[i]!=s[2*j-i] and s[j]!=s[2*j-i]:
                kom += 1


print(count-kom)