def xxx(N,K):
    if K==1:    return N-1
    sm,dd=1,1
    for n in range(10**9+1):
        if sm>=N:   return n
        dd *=K
        sm +=dd
    return -1

def main():
    Q=int(input())
    for i in range(Q):
        N,K=map(int,input().split())
        print(xxx(N,K))
    
main()