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']
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))