local n = io.read("*n", "*l")
local s = io.read()
local stack = {}
for w in s:gmatch("%g+") do
  if w == "+" then
    local v1 = stack[#stack - 1]
    local v2 = stack[#stack]
    stack[#stack - 1] = v1 + v2
    table.remove(stack)
  elseif w == "-" then
    local v1 = stack[#stack - 1]
    local v2 = stack[#stack]
    stack[#stack - 1] = v1 - v2
    table.remove(stack)
  else
    table.insert(stack, tonumber(w))
  end
end
print(stack[1])