n = int(input())
s = input().strip()

# Check if all characters are the same
if all(c == s[0] for c in s):
    print(1)
else:
    dp = [0] * (n + 1)
    last = {'R': -1, 'G': -1, 'B': -1}
    for i in range(n):
        c = s[i]
        option1 = dp[i] + 1
        if last[c] == -1:
            option2 = float('inf')
        else:
            option2 = dp[last[c] + 1] + 1
        dp[i + 1] = min(option1, option2)
        last[c] = i
    print(dp[n])