"use strict"

const arg_str = require('fs').readFileSync('/dev/stdin', 'UTF-8')
const args_lines = arg_str.split('\n')
const n = args_lines[0]
let a = []
const b = args_lines[1].split(' ')

b.forEach((item, index)=>{
    if(index == 0){
        a.push(b[0])
        return
    }
    if(b[index - 1] < b[index]){
        a.push(b[index - 1])
    }else{
        a.push(b[index])
    }
})
a.push(b[n-2])

console.log(a.reduce((a,b)=>(parseInt(a)+parseInt(b))))