'use strict';
function main(input) {
  const B = input.split('\n')[1].split(' ');
  let sum = parseInt(B[0]) + parseInt(B[B.length-1]);
  for (let i = 0; i < B.length-1; ++i) {
    sum += Math.min(parseInt(B[i]), parseInt(B[i+1]));
  }
  console.log(sum);
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));
