Buggy python submission (verdict: Time Limit Exceeded):
import sys
import math
from collections import deque
from decimal import Decimal, ROUND_HALF_UP, ROUND_HALF_EVEN
def I(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def S(): return sys.stdin.readline()
def LS(): return sys.stdin.readline().split()
def LS2(N): return [sys.stdin.readline().split() for i in range(N)]
def FILL(i,h,w): return [[i for j in range(w)] for k in range(h)]
def sisha(num,digit): return Decimal(str(num)).quantize(Decimal(digit),rounding=ROUND_HALF_UP)
#'0.01'や'1E1'などで指定、整数に戻すならintをかます
MOD = 1000000007
INF = float("inf")
sys.setrecursionlimit(10**6+10)
input = sys.stdin.readline

N = I()
S = input()
cnt = 0
l = [S[i] for i in range(N)]
for i in range(N-2):
    for j in range(i+1,N-1):
        for k in range(j+1,N):
            if l[i]==l[j] or l[j]==l[k] or l[k]==l[i] or j-i==k-j:
                continue
            cnt += 1

print(cnt)


Fixed submission:
import sys
import math
from collections import deque
from decimal import Decimal, ROUND_HALF_UP, ROUND_HALF_EVEN
def I(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def S(): return sys.stdin.readline()
def LS(): return sys.stdin.readline().split()
def LS2(N): return [sys.stdin.readline().split() for i in range(N)]
def FILL(i,h,w): return [[i for j in range(w)] for k in range(h)]
def sisha(num,digit): return Decimal(str(num)).quantize(Decimal(digit),rounding=ROUND_HALF_UP)
#'0.01'や'1E1'などで指定、整数に戻すならintをかます
MOD = 1000000007
INF = float("inf")
sys.setrecursionlimit(10**6+10)

input = sys.stdin.readline


N = I()
S = input().rstrip()
R = S.count('R')
G = S.count('G')
B = N-R-G

ans = R*G*B
for i in range(N):
    for j in range(i+1,N):
        if 2*j-i < N and S[i]!=S[j] and S[j]!=S[2*j-i] and S[2*j-i]!=S[i]:
            ans -= 1
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import math
from collections import deque
from decimal import Decimal, ROUND_HALF_UP, ROUND_HALF_EVEN
def I(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def S(): return sys.stdin.readline()
def LS(): return sys.stdin.readline().split()
def LS2(N): return [sys.stdin.readline().split() for i in range(N)]
def FILL(i,h,w): return [[i for j in range(w)] for k in range(h)]
def sisha(num,digit): return Decimal(str(num)).quantize(Decimal(digit),rounding=ROUND_HALF_UP)
#'0.01'や'1E1'などで指定、整数に戻すならintをかます
MOD = 1000000007
INF = float("inf")
sys.setrecursionlimit(10**6+10)
input = sys.stdin.readline

N = I()
S = input()
cnt = 0
for i in range(N-2):
    for j in range(i+1,N-1):
        for k in range(j+1,N):
            if S[i]==S[j] or S[j]==S[k] or S[k]==S[i] or j-i==k-j:
                continue
            cnt += 1

print(cnt)


Fixed submission:
import sys
import math
from collections import deque
from decimal import Decimal, ROUND_HALF_UP, ROUND_HALF_EVEN
def I(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI2(N): return [list(map(int, sys.stdin.readline().split())) for i in range(N)]
def S(): return sys.stdin.readline()
def LS(): return sys.stdin.readline().split()
def LS2(N): return [sys.stdin.readline().split() for i in range(N)]
def FILL(i,h,w): return [[i for j in range(w)] for k in range(h)]
def sisha(num,digit): return Decimal(str(num)).quantize(Decimal(digit),rounding=ROUND_HALF_UP)
#'0.01'や'1E1'などで指定、整数に戻すならintをかます
MOD = 1000000007
INF = float("inf")
sys.setrecursionlimit(10**6+10)

input = sys.stdin.readline


N = I()
S = input().rstrip()
R = S.count('R')
G = S.count('G')
B = N-R-G

ans = R*G*B
for i in range(N):
    for j in range(i+1,N):
        if 2*j-i < N and S[i]!=S[j] and S[j]!=S[2*j-i] and S[2*j-i]!=S[i]:
            ans -= 1
print(ans)