Problem p03137 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

template <class T> using V = vector<T>;
template <class T> using VV = V<V<T>>;
template <class T> using VVV = V<VV<T>>;
template <class T, class U> using P = pair<T, U>;
template <class S, class T, class U> using TUP = tuple<S, T, U>;

using ll = long long;
using ull = unsigned long long;
using dbl = double;
using str = string;
using vll = V<ll>;
using vll2 = VV<ll>;
using vll3 = VVV<ll>;
using pll = P<ll, ll>;
using tll = TUP<ll, ll, ll>;
using vpll = V<pll>;
using tpll = V<tll>;
using vs = V<str>;
using vvs = V<vs>;
using vd = V<dbl>;
using vvd = V<vd>;
using qll = queue<ll>;
using qpll = queue<pll>;
using mapll = map<ll, ll>;
using setll = set<ll>;

#define int ll
#define fst first
#define snd second
#define PQ priority_queue
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define popb pop_back()
#define sz size()
#define bn begin()
#define ed end()
#define FOR(i, a, b) for (ll i = (a); i <= (ll)(b); i++)
#define rFOR(i, a, b) for (ll i = (b); i >= (ll)(a); i--)
#define REP(i, n) FOR(i, 0, (n)-1)
#define REP1(i, n) FOR(i, 1, (n))
#define VFOR(i, v) for (auto &(i) : v)
#define IOTA(a, n)                                                             \
  vll(a)((n));                                                                 \
  iota((a).bn, (a).ed, (0));
#define SORT_ASC(a) sort((a).bn, (a).ed)
#define SORT_DESC(a) sort((a).rbegin(), (a).rend())
#define UNIQUE(a) (a).erase(unique((a).bn, (b).ed), (a).ed)
#define PREVP(a) prev_permutation((a).bn, (a).ed)
#define NEXTP(a) next_permutation((a).bn, (a).ed)
#define BINS(a, target) binary_search((a).bn, (a).ed, target)
#define LB(a, target) lower_bound((a).bn, (a).ed, target)
#define FIND(a, target) find((a).bn, (a).ed, target)
#define UB(a, target) upper_bound((a).bn, (a).ed, target)
#define CNT(a, target) count((a).bn, (a).ed, target)
#define SUM(a) accumulate((a).bn, (a).ed, 0)
#define DEBUG(...)                                                             \
  dal(#__VA_ARGS__);                                                           \
  dal(__VA_ARGS__)
#define Dig2(a, b) ((a) >> (b)&1)
#define Dig10(a, b) (ll)(((a) / ((ll)(pow(10.0, (dbl)(b))))) % 10)
#define DigN2(a) ((llabs(a) == 0) ? 1 : ((ll)log2((dbl)llabs(a)) + 1))
#define DigN10(a) ((llabs(a) == 0) ? 1 : ((ll)log10((dbl)llabs(a)) + 1))
#define Pow2(a) ((ll)(1) << (a))
#define Pow10(a) ((ll)(pow(10.0, double(a))))
#define LSB(a) ((a) & -(a))
#define llin(n)                                                                \
  ll n;                                                                        \
  cin >> n;
#define strin(n)                                                               \
  str n;                                                                       \
  cin >> n;
#define vin(v)                                                                 \
  VFOR(i, v) { cin >> (i); };
#define vllin(v, N)                                                            \
  vll(v)((N));                                                                 \
  vin(v);
#define vl4in(v1, v2, N)                                                       \
  vll(v1)(N), (v2)(N);                                                         \
  REP(i, N) { cin >> (v1)[i] >> (v2)[i]; };
#define vl6in(v1, v2, v3, N)                                                   \
  vll(v1)(N), (v2)(N), (v3)(N);                                                \
  REP(i, N) { cin >> (v1)[i] >> (v2)[i] >> (v3)[i]; };
#define vsin(v, N)                                                             \
  vs(v)((N));                                                                  \
  vin(v);
#define min(...) Min(__VA_ARGS__)
#define max(...) Max(__VA_ARGS__)
#define emin(a, ...) ((a) = Min((a), __VA_ARGS__))
#define emax(a, ...) ((a) = Max((a), __VA_ARGS__))
#define egcd(a, ...) ((a) = gcd((a), __VA_ARGS__))
#define elcm(a, ...) ((a) = lcm((a), __VA_ARGS__))
#define tf(cond, t, f)                                                         \
  if (cond) {                                                                  \
    echo(t);                                                                   \
  } else {                                                                     \
    echo(f);                                                                   \
  }
#define yn(cond) tf(cond, "yes", "no")
#define Yn(cond) tf(cond, "Yes", "No")
#define YN(cond) tf(cond, "YES", "NO")

static const ll MOD = (ll)1e9 + 7;
static const ll INF = (1LL << 62) - 1; // 4.611E+18
static const dbl PI = acos(-1.0);

void Input(){};
template <class T, class... Args> void Input(T &t, Args &...args) {
  cin >> t;
  Input(args...);
}

void vInit(ll size) {}
template <class T, class... Args> void vInit(ll size, V<T> &v, Args &...args) {
  v.resize(size);
  vInit(size, args...);
}

void vInputNum(ll num) {}
template <class T, class... Args>
void vInputNum(ll num, V<T> &v, Args &...args) {
  cin >> v[num];
  vInputNum(num, args...);
}

void vInput(ll size) {}
template <class... Args> void vInput(ll size, Args &...args) {
  vInit(size);
  REP(i, size) { vInputNum(i, args...); }
}

template <class S, class T> ostream &operator<<(ostream &o, const P<S, T> &p) {
  return o << "(" << p.first << ", " << p.second << ")";
}

template <class T> ostream &operator<<(ostream &o, const V<T> &v) {
  if (v.empty()) {
    return o << "[]";
  } else {
    auto itr = v.bn;
    o << "[" << *itr;
    itr++;
    while (itr != v.ed) {
      o << ", " << *itr;
      itr++;
    }
    o << "]";
    return o;
  }
}

template <class T> ostream &operator<<(ostream &o, queue<T> q) {
  if (q.empty()) {
    return o << "| |";
  } else {
    while (!q.empty()) {
      o << "| " << q.front() << " ";
      q.pop();
    }
    o << "|";
    return o;
  }
}

template <class S, class T>
ostream &operator<<(ostream &o, const map<S, T> &m) {
  if (m.empty()) {
    return o << "[]";
  } else {
    auto itr = m.bn;
    o << "{" << itr->first << ": " << itr->second;
    itr++;
    while (itr != m.ed) {
      o << "} {" << itr->first << ": " << itr->second;
      itr++;
    }
    o << "}";
    return o;
  }
}

template <class T> ostream &operator<<(ostream &o, const set<T> &s) {
  if (s.empty()) {
    return o << "<>";
  } else {
    auto itr = s.bn;
    o << "<" << *itr;
    itr++;
    while (itr != s.ed) {
      o << ", " << *itr;
      itr++;
    }
    o << ">";
    return o;
  }
}

void say() {}
template <class T> void say(T t) { cout << t; }
template <class Head, class... Body> void say(Head h, Body... b) {
  cout << h;
  say(b...);
}
void echo() { cout << "\n"; }
template <class... Args> void echo(Args... args) {
  say(args...);
  cout << "\n";
}

void dbgsay() {}
template <class T> void dbgsay(T t) { cout << t; }
template <class Head, class... Body> void dbgsay(Head h, Body... b) {
  cerr << h << " ";
  dbgsay(b...);
}
void dbgecho() { cout << "\n"; }
template <class... Args> void dbgecho(Args... args) {
  dbgsay(args...);
  cerr << "\n";
}

void echovv() {}
template <class T> void echovv(VV<T> v) {
  if (v.empty()) {
    echo();
  } else {
    VFOR(i, v)
    echo(v);
  }
}
template <class T, class... Args> void echovv(VV<T> v, Args... args) {
  echovv(v);
  echovv(args...);
}
template <class Head> Head Min(Head head) { return head; }
template <class Head, class... Body> Head Min(Head h, Body... b) {
  auto t = Min(b...);
  return (h < t) ? h : t;
}
template <class Head> Head Max(Head head) { return head; }
template <class Head, class... Body> Head Max(Head h, Body... b) {
  auto t = Max(b...);
  return (h > t) ? h : t;
}

ll gcd(ll a, ll b) {
  if (a < b) {
    a ^= b;
    b ^= a;
    a ^= b;
  }
  return b ? gcd(b, a % b) : a;
}
template <class... Body> ll gcd(ll h, Body... b) { return gcd(h, gcd(b...)); }

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <class... Body> ll lcm(ll h, Body... b) { return lcm(h, lcm(b...)); }

ll Bset(ll a, ll b, ll c) {
  if (c)
    a |= b;
  else
    a &= ~b;
  return a;
}

struct UF {
public:
  ll tsize;
  ll mode;
  vll par;
  vll rank;
  UF(){};
  UF(const UF &uf) {}
  UF(ll _size, ll _mode = 0) {
    tsize = _size;
    mode = _mode;
    par.assign(tsize, -1);
    if (!mode)
      rank.resize(tsize, 0);
  }
  ll root(ll x) { return par[x] < 0 ? x : par[x] = root(par[x]); }
  bool isRoot(ll x) { return root(x) == x; }
  void unite(ll x, ll y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (mode) {
      par[x] += par[y];
      par[y] += x;
    } else {
      if (rank[x] < rank[y]) {
        par[y] += par[x];
        par[x] = y;
      } else {
        par[x] += par[y];
        par[y] = x;
        if (rank[x] == rank[y])
          rank[x]++;
      }
    }
  }
  bool same(ll x, ll y) { return root(x) == root(y); }
  ll size(ll x) { return -par[root(x)]; }
};

class Vertex {
public:
  ll idx;
  ll param = -1;
  ll dist = INF;
  vector<pair<Vertex *, ll> /**/> e;
  ll size() { return e.size(); }
  bool operator==(const Vertex *o) { return dist == o->dist; }
  bool operator!=(const Vertex *o) { return dist != o->dist; }
  bool operator>(const Vertex *o) { return dist > o->dist; }
  bool operator<(const Vertex *o) { return dist < o->dist; }
  bool operator>=(const Vertex *o) { return dist >= o->dist; }
  bool operator<=(const Vertex *o) { return dist <= o->dist; }
};

class Graph {
public:
  vector<Vertex *> V;
  vll order;
  typedef tuple<Vertex *, Vertex *, ll> Edge;
  vector<Edge> E;
  Graph(ll siz) {
    REP(i, siz) {
      auto v = new Vertex();
      v->idx = i;
      V.pb(v);
    }
  }
  static bool comp(const Edge &e1, const Edge &e2) {
    return get<2>(e1) < get<2>(e2);
  }
  Vertex *getVertex(ll idx) { return V[idx]; }
  void unite(ll from, ll to, ll w = 1, bool digraph = true) {
    E.push_back(make_tuple(V[from], V[to], w));
    V[from]->e.pb(make_pair(V[to], w));
    if (!digraph) {
      E.push_back(make_tuple(V[to], V[from], w));
      V[to]->e.pb(make_pair(V[from], w));
    }
  }
  void dijkstra(ll start) {
    PQ<Vertex *, vector<Vertex *>, greater<Vertex *> /**/> pq;
    Vertex *s = getVertex(start);
    s->dist = 0;
    pq.push(s);
    while (!pq.empty()) {
      Vertex *v = pq.top();
      pq.pop();
      for (auto &u : v->e) {
        if (u.first->dist > v->dist + u.second) {
          u.first->dist = v->dist + u.second;
          pq.push(u.first);
        }
      }
    }
  }
  bool sort() {
    for (auto &v : V) {
      if (v->param == -1 && !sort_visit(v->idx)) {
        return false;
      }
    }
    reverse(order.bn, order.ed);
    return true;
  }
  bool sort_visit(int v) {
    Vertex *_v = getVertex(v);
    _v->param = 1;
    if (!_v->e.empty()) {
      for (auto &u : _v->e) {
        if (u.first->param == 2)
          continue;
        if (u.first->param == 1)
          return false;
        if (!sort_visit(u.first->idx))
          return false;
      }
    }
    order.push_back(v);
    _v->param = 2;
    return true;
  }
};

ll isPrime(ll n) {
  if (n <= 1)
    return 0;
  FOR(i, 2, (ll)sqrt(n)) {
    if (n % i == 0)
      return 0;
  }
  return 1;
}

ll DigS10(ll n) {
  ll m = 0;
  REP(i, DigN10(n)) { m += (ll)((llabs(n) % Pow10(i + 1))) / Pow10(i); }
  return m;
}

ll PowMod(ll a, ll b) {
  ll ans = 1, x = a % MOD;
  REP(i, DigN2(b)) {
    if (Dig2(b, i) == 1) {
      ans = (ans * x) % MOD;
    }
    if (i != (DigN2(b) - 1)) {
      x = (x * x) % MOD;
    }
  }
  return ans;
}

vll FactMod(1, 1);
vll FactModInv(1, 1);
ll Mod(ll n) {
  n %= MOD;
  n = (n + MOD) % MOD;
  return n;
}
ll InvM(ll n) {
  n = Mod(n);
  n = PowMod(n, MOD - 2);
  return n;
}
void CFactMod(ll n) {
  if (FactMod.size() <= n) {
    FOR(i, FactMod.size(), n) {
      FactMod.pb((FactMod[i - 1] * (i % MOD)) % MOD);
    }
  }
}
void CFactModInv(ll n) {
  CFactMod(n);
  if (FactModInv.size() < (n + 1)) {
    FactModInv.resize(n + 1, -1);
  }
  if (FactModInv[n] == -1) {
    FactModInv[n] = PowMod(FactMod[n], MOD - 2);
  }
  for (int i = n - 1; i >= 1; i--) {
    if (FactModInv[i] != -1)
      break;
    FactModInv[i] = ((FactModInv[i + 1] * ((i + 1) % MOD)) % MOD);
  }
}

ll CombMod(ll n, ll k) {
  if (n < 0 || k < 0 || n < k)
    return 0;
  if (n + 1 > FactModInv.size())
    CFactModInv(n);
  return ((((FactModInv[k] * FactModInv[n - k]) % MOD) * FactMod[n]) % MOD);
}

pll factor_sub(ll n, ll m) {
  ll i = 0;
  while (n % m == 0) {
    i++;
    n /= m;
  }
  return mp(i, n);
}

vpll factrization(ll n) {
  vpll a;
  ll c, m;
  tie(c, m) = factor_sub(n, 2);
  if (c > 0)
    a.pb(mp(2, c));
  for (ll i = 3; m >= i * i; i += 2) {
    tie(c, m) = factor_sub(m, i);
    if (c > 0)
      a.pb(mp(i, c));
  }
  if (m > 1)
    a.pb(mp(m, 1));
  return a;
}

signed main() {
  llin(N);
  llin(M);
  vllin(X, M);
  SORT_ASC(X);
  vll y;
  if (M == 1) {
    echo(0);
    return 0;
  }
  REP(i, M - 1) { y.pb(abs(X[i] - X[i + 1])); }
  SORT_DESC(y);
  FOR(i, 0, N - 2) { y.erase(y.bn + 0); }
  echo(SUM(y));
}

Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;

template <class T> using V = vector<T>;
template <class T> using VV = V<V<T>>;
template <class T> using VVV = V<VV<T>>;
template <class T, class U> using P = pair<T, U>;
template <class S, class T, class U> using TUP = tuple<S, T, U>;

using ll = long long;
using ull = unsigned long long;
using dbl = double;
using str = string;
using vll = V<ll>;
using vll2 = VV<ll>;
using vll3 = VVV<ll>;
using pll = P<ll, ll>;
using tll = TUP<ll, ll, ll>;
using vpll = V<pll>;
using tpll = V<tll>;
using vs = V<str>;
using vvs = V<vs>;
using vd = V<dbl>;
using vvd = V<vd>;
using qll = queue<ll>;
using qpll = queue<pll>;
using mapll = map<ll, ll>;
using setll = set<ll>;

#define int ll
#define fst first
#define snd second
#define PQ priority_queue
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define popb pop_back()
#define sz size()
#define bn begin()
#define ed end()
#define FOR(i, a, b) for (ll i = (a); i <= (ll)(b); i++)
#define rFOR(i, a, b) for (ll i = (b); i >= (ll)(a); i--)
#define REP(i, n) FOR(i, 0, (n)-1)
#define REP1(i, n) FOR(i, 1, (n))
#define VFOR(i, v) for (auto &(i) : v)
#define IOTA(a, n)                                                             \
  vll(a)((n));                                                                 \
  iota((a).bn, (a).ed, (0));
#define SORT_ASC(a) sort((a).bn, (a).ed)
#define SORT_DESC(a) sort((a).rbegin(), (a).rend())
#define UNIQUE(a) (a).erase(unique((a).bn, (b).ed), (a).ed)
#define PREVP(a) prev_permutation((a).bn, (a).ed)
#define NEXTP(a) next_permutation((a).bn, (a).ed)
#define BINS(a, target) binary_search((a).bn, (a).ed, target)
#define LB(a, target) lower_bound((a).bn, (a).ed, target)
#define FIND(a, target) find((a).bn, (a).ed, target)
#define UB(a, target) upper_bound((a).bn, (a).ed, target)
#define CNT(a, target) count((a).bn, (a).ed, target)
#define SUM(a) accumulate((a).bn, (a).ed, 0)
#define DEBUG(...)                                                             \
  dal(#__VA_ARGS__);                                                           \
  dal(__VA_ARGS__)
#define Dig2(a, b) ((a) >> (b)&1)
#define Dig10(a, b) (ll)(((a) / ((ll)(pow(10.0, (dbl)(b))))) % 10)
#define DigN2(a) ((llabs(a) == 0) ? 1 : ((ll)log2((dbl)llabs(a)) + 1))
#define DigN10(a) ((llabs(a) == 0) ? 1 : ((ll)log10((dbl)llabs(a)) + 1))
#define Pow2(a) ((ll)(1) << (a))
#define Pow10(a) ((ll)(pow(10.0, double(a))))
#define LSB(a) ((a) & -(a))
#define llin(n)                                                                \
  ll n;                                                                        \
  cin >> n;
#define strin(n)                                                               \
  str n;                                                                       \
  cin >> n;
#define vin(v)                                                                 \
  VFOR(i, v) { cin >> (i); };
#define vllin(v, N)                                                            \
  vll(v)((N));                                                                 \
  vin(v);
#define vl4in(v1, v2, N)                                                       \
  vll(v1)(N), (v2)(N);                                                         \
  REP(i, N) { cin >> (v1)[i] >> (v2)[i]; };
#define vl6in(v1, v2, v3, N)                                                   \
  vll(v1)(N), (v2)(N), (v3)(N);                                                \
  REP(i, N) { cin >> (v1)[i] >> (v2)[i] >> (v3)[i]; };
#define vsin(v, N)                                                             \
  vs(v)((N));                                                                  \
  vin(v);
#define min(...) Min(__VA_ARGS__)
#define max(...) Max(__VA_ARGS__)
#define emin(a, ...) ((a) = Min((a), __VA_ARGS__))
#define emax(a, ...) ((a) = Max((a), __VA_ARGS__))
#define egcd(a, ...) ((a) = gcd((a), __VA_ARGS__))
#define elcm(a, ...) ((a) = lcm((a), __VA_ARGS__))
#define tf(cond, t, f)                                                         \
  if (cond) {                                                                  \
    echo(t);                                                                   \
  } else {                                                                     \
    echo(f);                                                                   \
  }
#define yn(cond) tf(cond, "yes", "no")
#define Yn(cond) tf(cond, "Yes", "No")
#define YN(cond) tf(cond, "YES", "NO")

static const ll MOD = (ll)1e9 + 7;
static const ll INF = (1LL << 62) - 1; // 4.611E+18
static const dbl PI = acos(-1.0);

void Input(){};
template <class T, class... Args> void Input(T &t, Args &...args) {
  cin >> t;
  Input(args...);
}

void vInit(ll size) {}
template <class T, class... Args> void vInit(ll size, V<T> &v, Args &...args) {
  v.resize(size);
  vInit(size, args...);
}

void vInputNum(ll num) {}
template <class T, class... Args>
void vInputNum(ll num, V<T> &v, Args &...args) {
  cin >> v[num];
  vInputNum(num, args...);
}

void vInput(ll size) {}
template <class... Args> void vInput(ll size, Args &...args) {
  vInit(size);
  REP(i, size) { vInputNum(i, args...); }
}

template <class S, class T> ostream &operator<<(ostream &o, const P<S, T> &p) {
  return o << "(" << p.first << ", " << p.second << ")";
}

template <class T> ostream &operator<<(ostream &o, const V<T> &v) {
  if (v.empty()) {
    return o << "[]";
  } else {
    auto itr = v.bn;
    o << "[" << *itr;
    itr++;
    while (itr != v.ed) {
      o << ", " << *itr;
      itr++;
    }
    o << "]";
    return o;
  }
}

template <class T> ostream &operator<<(ostream &o, queue<T> q) {
  if (q.empty()) {
    return o << "| |";
  } else {
    while (!q.empty()) {
      o << "| " << q.front() << " ";
      q.pop();
    }
    o << "|";
    return o;
  }
}

template <class S, class T>
ostream &operator<<(ostream &o, const map<S, T> &m) {
  if (m.empty()) {
    return o << "[]";
  } else {
    auto itr = m.bn;
    o << "{" << itr->first << ": " << itr->second;
    itr++;
    while (itr != m.ed) {
      o << "} {" << itr->first << ": " << itr->second;
      itr++;
    }
    o << "}";
    return o;
  }
}

template <class T> ostream &operator<<(ostream &o, const set<T> &s) {
  if (s.empty()) {
    return o << "<>";
  } else {
    auto itr = s.bn;
    o << "<" << *itr;
    itr++;
    while (itr != s.ed) {
      o << ", " << *itr;
      itr++;
    }
    o << ">";
    return o;
  }
}

void say() {}
template <class T> void say(T t) { cout << t; }
template <class Head, class... Body> void say(Head h, Body... b) {
  cout << h;
  say(b...);
}
void echo() { cout << "\n"; }
template <class... Args> void echo(Args... args) {
  say(args...);
  cout << "\n";
}

void dbgsay() {}
template <class T> void dbgsay(T t) { cout << t; }
template <class Head, class... Body> void dbgsay(Head h, Body... b) {
  cerr << h << " ";
  dbgsay(b...);
}
void dbgecho() { cout << "\n"; }
template <class... Args> void dbgecho(Args... args) {
  dbgsay(args...);
  cerr << "\n";
}

void echovv() {}
template <class T> void echovv(VV<T> v) {
  if (v.empty()) {
    echo();
  } else {
    VFOR(i, v)
    echo(v);
  }
}
template <class T, class... Args> void echovv(VV<T> v, Args... args) {
  echovv(v);
  echovv(args...);
}
template <class Head> Head Min(Head head) { return head; }
template <class Head, class... Body> Head Min(Head h, Body... b) {
  auto t = Min(b...);
  return (h < t) ? h : t;
}
template <class Head> Head Max(Head head) { return head; }
template <class Head, class... Body> Head Max(Head h, Body... b) {
  auto t = Max(b...);
  return (h > t) ? h : t;
}

ll gcd(ll a, ll b) {
  if (a < b) {
    a ^= b;
    b ^= a;
    a ^= b;
  }
  return b ? gcd(b, a % b) : a;
}
template <class... Body> ll gcd(ll h, Body... b) { return gcd(h, gcd(b...)); }

ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <class... Body> ll lcm(ll h, Body... b) { return lcm(h, lcm(b...)); }

ll Bset(ll a, ll b, ll c) {
  if (c)
    a |= b;
  else
    a &= ~b;
  return a;
}

struct UF {
public:
  ll tsize;
  ll mode;
  vll par;
  vll rank;
  UF(){};
  UF(const UF &uf) {}
  UF(ll _size, ll _mode = 0) {
    tsize = _size;
    mode = _mode;
    par.assign(tsize, -1);
    if (!mode)
      rank.resize(tsize, 0);
  }
  ll root(ll x) { return par[x] < 0 ? x : par[x] = root(par[x]); }
  bool isRoot(ll x) { return root(x) == x; }
  void unite(ll x, ll y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return;
    if (mode) {
      par[x] += par[y];
      par[y] += x;
    } else {
      if (rank[x] < rank[y]) {
        par[y] += par[x];
        par[x] = y;
      } else {
        par[x] += par[y];
        par[y] = x;
        if (rank[x] == rank[y])
          rank[x]++;
      }
    }
  }
  bool same(ll x, ll y) { return root(x) == root(y); }
  ll size(ll x) { return -par[root(x)]; }
};

class Vertex {
public:
  ll idx;
  ll param = -1;
  ll dist = INF;
  vector<pair<Vertex *, ll> /**/> e;
  ll size() { return e.size(); }
  bool operator==(const Vertex *o) { return dist == o->dist; }
  bool operator!=(const Vertex *o) { return dist != o->dist; }
  bool operator>(const Vertex *o) { return dist > o->dist; }
  bool operator<(const Vertex *o) { return dist < o->dist; }
  bool operator>=(const Vertex *o) { return dist >= o->dist; }
  bool operator<=(const Vertex *o) { return dist <= o->dist; }
};

class Graph {
public:
  vector<Vertex *> V;
  vll order;
  typedef tuple<Vertex *, Vertex *, ll> Edge;
  vector<Edge> E;
  Graph(ll siz) {
    REP(i, siz) {
      auto v = new Vertex();
      v->idx = i;
      V.pb(v);
    }
  }
  static bool comp(const Edge &e1, const Edge &e2) {
    return get<2>(e1) < get<2>(e2);
  }
  Vertex *getVertex(ll idx) { return V[idx]; }
  void unite(ll from, ll to, ll w = 1, bool digraph = true) {
    E.push_back(make_tuple(V[from], V[to], w));
    V[from]->e.pb(make_pair(V[to], w));
    if (!digraph) {
      E.push_back(make_tuple(V[to], V[from], w));
      V[to]->e.pb(make_pair(V[from], w));
    }
  }
  void dijkstra(ll start) {
    PQ<Vertex *, vector<Vertex *>, greater<Vertex *> /**/> pq;
    Vertex *s = getVertex(start);
    s->dist = 0;
    pq.push(s);
    while (!pq.empty()) {
      Vertex *v = pq.top();
      pq.pop();
      for (auto &u : v->e) {
        if (u.first->dist > v->dist + u.second) {
          u.first->dist = v->dist + u.second;
          pq.push(u.first);
        }
      }
    }
  }
  bool sort() {
    for (auto &v : V) {
      if (v->param == -1 && !sort_visit(v->idx)) {
        return false;
      }
    }
    reverse(order.bn, order.ed);
    return true;
  }
  bool sort_visit(int v) {
    Vertex *_v = getVertex(v);
    _v->param = 1;
    if (!_v->e.empty()) {
      for (auto &u : _v->e) {
        if (u.first->param == 2)
          continue;
        if (u.first->param == 1)
          return false;
        if (!sort_visit(u.first->idx))
          return false;
      }
    }
    order.push_back(v);
    _v->param = 2;
    return true;
  }
};

ll isPrime(ll n) {
  if (n <= 1)
    return 0;
  FOR(i, 2, (ll)sqrt(n)) {
    if (n % i == 0)
      return 0;
  }
  return 1;
}

ll DigS10(ll n) {
  ll m = 0;
  REP(i, DigN10(n)) { m += (ll)((llabs(n) % Pow10(i + 1))) / Pow10(i); }
  return m;
}

ll PowMod(ll a, ll b) {
  ll ans = 1, x = a % MOD;
  REP(i, DigN2(b)) {
    if (Dig2(b, i) == 1) {
      ans = (ans * x) % MOD;
    }
    if (i != (DigN2(b) - 1)) {
      x = (x * x) % MOD;
    }
  }
  return ans;
}

vll FactMod(1, 1);
vll FactModInv(1, 1);
ll Mod(ll n) {
  n %= MOD;
  n = (n + MOD) % MOD;
  return n;
}
ll InvM(ll n) {
  n = Mod(n);
  n = PowMod(n, MOD - 2);
  return n;
}
void CFactMod(ll n) {
  if (FactMod.size() <= n) {
    FOR(i, FactMod.size(), n) {
      FactMod.pb((FactMod[i - 1] * (i % MOD)) % MOD);
    }
  }
}
void CFactModInv(ll n) {
  CFactMod(n);
  if (FactModInv.size() < (n + 1)) {
    FactModInv.resize(n + 1, -1);
  }
  if (FactModInv[n] == -1) {
    FactModInv[n] = PowMod(FactMod[n], MOD - 2);
  }
  for (int i = n - 1; i >= 1; i--) {
    if (FactModInv[i] != -1)
      break;
    FactModInv[i] = ((FactModInv[i + 1] * ((i + 1) % MOD)) % MOD);
  }
}

ll CombMod(ll n, ll k) {
  if (n < 0 || k < 0 || n < k)
    return 0;
  if (n + 1 > FactModInv.size())
    CFactModInv(n);
  return ((((FactModInv[k] * FactModInv[n - k]) % MOD) * FactMod[n]) % MOD);
}

pll factor_sub(ll n, ll m) {
  ll i = 0;
  while (n % m == 0) {
    i++;
    n /= m;
  }
  return mp(i, n);
}

vpll factrization(ll n) {
  vpll a;
  ll c, m;
  tie(c, m) = factor_sub(n, 2);
  if (c > 0)
    a.pb(mp(2, c));
  for (ll i = 3; m >= i * i; i += 2) {
    tie(c, m) = factor_sub(m, i);
    if (c > 0)
      a.pb(mp(i, c));
  }
  if (m > 1)
    a.pb(mp(m, 1));
  return a;
}

signed main() {
  llin(N);
  llin(M);
  vllin(X, M);
  SORT_ASC(X);
  vll y;
  if (M == 1 || N >= M) {
    echo(0);
    return 0;
  }
  REP(i, M - 1) { y.pb(abs(X[i] - X[i + 1])); }
  SORT_DESC(y);
  FOR(i, 0, N - 2) { y.erase(y.bn + 0); }
  echo(SUM(y));
}