log = console.log;

var stdin = require("fs").readFileSync("/dev/stdin", "UTF-8");
var lines = stdin.split("\n");
var N = lines[0].split(" ")[0];
var M = lines[0].split(" ")[1];
var XS = lines[1].split(" ");

if (N >= M) {
  log(0);
} else {
  XS = XS.sort((a, b) => {
    return +a - +b;
  });

  LS = [];
  for (var i = 0; i < XS.length - 1; i++) {
    var L = XS[i + 1] - XS[i];
    LS.push(L);
  }

  LS.sort((a,b)=> a - b)
  sum = LS.slice(0,M-N).reduce((a,c)=> a+c)

  log(sum)
}