local n = io.read("*n")
local a = {}
for i = 1, n do
  a[i] = io.read("*n")
end
a[n + 1] = -1
local len = 1
local ret = 0
for i = 1, n do
  if a[i] + 1 ~= a[i + 1] then
    len = 1
  else
    ret = ret + len
    len = len + 1
  end
end
print(ret)