local mmi, mma = math.min, math.max
local n = io.read("*n")
local perf, spare = io.read("*n", "*n")
for i = 2, n do
  local p, s = io.read("*n", "*n")
  perf, spare = mma(perf + p, spare + p * 2), mma(perf + s, spare + s * 2)
end
print(mma(perf, spare))