n = input().split()
x = int(n[0])
y = int(n[1])
z = int(n[2])
a = x + y + z
print("%.3f" % (a / 3))
/**************************************************************
	Problem: 1957
	User: admin
	Language: Python
	Result: Accepted
	Time:117 ms
	Memory:34244 kb
****************************************************************/