def beauty(x):
    for i in range(3):
        for j in range(i + 3, len(x), 3):
            if x[j] != x[j - 3]:
                return False
    return True


n = int(input())
l = input()
lamps = []
for i in l:
    lamps.append(i)
res = 0
c = 0
C = []
K1 = [0, 1, 2]
K2 = ['G', 'R', 'B']
if beauty(lamps) == True:
    res = 0
else:
    for i in range(3, n):
        if lamps[i] == lamps[i - 3]:
            c += 1
            C.append(i % 3)
            S.append((i, lamps[i]))
    if c == 0:
        pass
    else:
        for i in range(len(S) % 3):
            K1.remove(i % 3)
            K2.remove(S[i][1])
            for j in range(i % 3, n, 3):
                if lamps[j] != S[i][1]:
                    lamps[j] = S[i][1]
                    res += 1
    j = 0
    while len(K1) != 0:
        for i in range(K1[j], n, 3):
            if lamps[i] != K2[0]:
                lamps[i] = K2[0]
                res += 1
        K1.pop(j)
        K2.pop(0)
print(res)
print(''.join(lamps))