const main = B => {
    const max = Math.max(...B)
    var ans = 0
    const A = []
    for(var i =0;i<B.length-1;i++ ) {
        A.push(Math.min(B[i],B[i+1]))
    }
    return A.reduce((acm,current) => {return acm + current},0)+B[0]+B[B.length-1]
}

const input = require('fs').readFileSync('/dev/stdin','utf8').split("\n")
const N = Number(input[0])
const B = input[1].split(" ").map(x => Number(x))
console.log(main(B))