n=int(input())
a=n//1000
b=n//100%10
c=n//10%10
d=n%10
print("%.2f"%((n+(a*10+b)+(c*10+d))/3))
/**************************************************************
	Problem: 1618
	User: admin
	Language: Python
	Result: Accepted
	Time:95 ms
	Memory:34244 kb
****************************************************************/