a,b,c=map(int,input().split(" "))
if a**2+b**2==c**2:
    s=0.5*a*b
    print("%.1f"%s)
elif a**2+c**2==b**2:
    s=0.5*a*c
    print("%.1f"%s)
elif b**2+c**2==a**2:
    s=0.5*b*c
    print("%.1f"%s)
else:
    print("No")
/**************************************************************
	Problem: 1047
	User: admin
	Language: Python
	Result: Accepted
	Time:134 ms
	Memory:34480 kb
****************************************************************/