Python 3.6


a=int(input())
if a<=4 and a>=1:
    print("few")
    if a<=9 and A>=5:
        print("several")
        if a<=19 and a>=10:
            print("pack")
            if a<=49 and a>=20:
                print("lots")
                if a<=99 and a>=50:
                    print("horde")
                    if a<=249 and a>=100:
                        print("throng")
                        if a<=499 and a>=250:
                            print("swarm")
                            if a<=999 and a>=500:
                                print("zounds")
                                if a>=1000:
                                    print("legion")

Попробуй другие отступы

num_monst = int (input ("Write number of monster"))

if  1 <= num_monst <= 4:
    print("few")

elif  5 <= num_monst <= 9:
    print("several")

elif 10 <= num_monst <= 19 :
    print("lots")

elif  20 <= num_monst <= 49 :
    print("horde")

elif  50 <= num_monst <= 99 :
    print("throng")

elif  100 <= num_monst <= 249 :
    print("swarm")

elif  250 <= num_monst <= 999 :
    print("zounds")

elif  num_monst >= 1000 :
    print("legion")