def min_replacements(n, S, T):
   
    replacements = 0
    for i in range(n):
        if S[i] != T[i]:
            replacements += 1
    return replacements


if __name__ == "__main__":
    n = int(input().strip())
    S = input().strip()
    T = input().strip()
    result = min_replacements(n, S, T)
    print(result)