local ffi = require 'ffi'
local C = ffi.C
ffi.cdef 'int scanf(const char *, ...);'

do 
local cd,a=ffi.new("int8_t[1]"),{}
for _=1,io.stdin:read("*n") do
	C.scanf(" %c",cd) a[1]=cd[0]-48
	for i=2,1000 do
		C.scanf("%c",cd) if cd[0]==10 then break end a[i]=cd[0]-48
		a[i-1]=a[i-1]+a[i]>9 and a[i-1]+a[i]-9 or a[i-1]+a[i]
	end if #a>1 then a[#a]=nil end
	while #a>1 do
		for i=2,#a do
			a[i-1]=a[i-1]+a[i]>9 and a[i-1]+a[i]-9 or a[i-1]+a[i]
		end a[#a]=nil
	end
	io.write(a[1],"\n")
end
end