Parenting Partnering Returns

t = int(input())
i = 0

while(i<t):
    start = list()
    end = list()
    start_1 = list()
    n = int(input())
    J = -1
    C = -1
    s_1 = list()
    s_2 = list()
    imp = 0
    s=""
    for j in range(n):
        ele = input()
        a = ele.split(" ")
        start_1.append(int(a[0]))
        if(j == 0):
            start.append(int(a[0]))
            end.append(int(a[1]))
        else:
            for k in range(len(start)):
                if(int(a[0])<start[k]):
                    start.insert(k,int(a[0]))
                    end.insert(k,int(a[1]))
                    break
                elif(k == len(start)-1):
                    start.append(int(a[0]))
                    end.append(int(a[1]))
    for k in range(len(start)):
        if(k==0):
            J=k
            s_1.append(start_1.index(start[k]))
        else:
            if(start[k]<end[J]):
                if(start[k]>=end[C] or C==-1):
                    C=k
                    s_2.append(start_1.index(start[k]))
                else:
                    imp = 1
                    break
            elif(start[k]>=end[J]):
                J=k
                s_1.append(start_1.index(start[k]))
    i+=1
    if(imp == 1):
        print("Case #%d: IMPOSSIBLE"%(i))
        imp = 0
    else:
        temp = 0
        while(temp<n):
            if(temp in s_1):
                s += "J"
            else:
                s += "C"
            temp += 1
        print("Case #%d:"%(i),s)
    start.clear()
    end.clear()
    start_1.clear()
    s_1.clear()
    s_2.clear()
    s=""