var main = function main(input) {
  var args = input.split(' ')
  var average = (+args[0] + +args[1]) / 2
  var point = average % 1
  if (point >= 0.5) {
      average = average + 0.5
      var point2 = average % 1
      average = average - point2
  } else {
      average = average - point
  }
  console.log(average)
}
 
main(require('fs').readFileSync('/dev/stdin', 'utf-8'))
