import sys
input = sys.stdin.readline

T=int(input())
for tests in range(T):
    M,R,N=map(int,input().split())
    X=list(map(int,input().split()))

    X.append(1<<63)

    ANS=0
    last=R

    for i in range(N):
        if X[i]>last:
            ANS="IMPOSSIBLE"
            break
        if X[i]<=last and X[i+1]<=last:
            continue
        if X[i]<=last and X[i+1]>last:
            ANS+=1
            last=X[i]+R+R

            if X[i]+R>=M:
                break

    if last-R>=M:
        print("Case #"+str(tests+1)+": "+str(ANS))
    else:
        print("Case #"+str(tests+1)+": "+"IMPOSSIBLE")