N = io.read("*n")
B = {}
for i = 1, N-1 do
    B[i] = io.read("*n")
end

A = {}
for i = 1, N do
    if i == 1 then
        A[i] = B[i]
    elseif i == N then
        A[i] = B[i-1]
    else
        A[i] = math.min(B[i-1], B[i])
    end
end

sum = 0
for i = 1, N do
    sum = sum + A[i]
end
print(sum)