function main(input) {
  var rows = input.split('\n');
  var pieceCount = rows[0].split(" ").map(Number)[0];
  var coordinates = rows[1].trim().split(" ").map(Number).sort((a, b) => a - b);

  if (pieceCount >= coordinates.length){
    console.log(0);
    return;
  }

  var steps = [];
  coordinates.forEach((item, i) => {
      if (i > 0) {
      steps.push(item - coordinates[i-1])
      }
  })
  steps = steps.sort((a, b) => a - b).slice(0, steps.length - pieceCount + 1);
  console.log(steps.reduce((sum, cur) => sum+cur, 0))
}

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