input = require("fs").readFileSync("/dev/stdin", "utf8")

lines = input.split("\n")
N = lines.shift() * 1
B = lines.shift().split(' ').map(function(i) { return i * 1 })

ans = 0
ans += B[0]
ans += B[N-2]
for (i = 1; i < N - 1; i++) {
  min = Math.min(B[i], B[i-1])
  ans += min
}

console.log(ans)
