#include <bits/stdc++.h>
#define rep(x, to) for (int x = 0; x < (to); x++)
#define REP(x, a, to) for (int x = (a); x < (to); x++)
#define EPS (1e-14)
#define _PA(x,N) rep(i,N){cout<<x[i]<<" ";}cout<<endl;
#define _PA2(x,H,W) rep(i,(H)){rep(j,(W)){cout<<x[i][j]<<" ";}cout<<endl;}

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;
typedef complex<double> Complex;
typedef vector< vector<int> > Mat;

int N, M;
int D[1005];

int ans = 1e+9 + 7;

void solve() {
	sort(D + 1, D + M + 1);
	for (int i = N; i <= M; i++) {
		int p = D[i - N + 1];
		int q = D[i];
		if (p > 0) {
			ans = min(ans, (q - p) + abs(p));
		} else if (q < 0) {
			ans = min(ans, (q - p) + abs(q));
		} else {
			ans = min(ans, (q - p) + min(abs(p), abs(q)));
		}
	}
	cout << ans << endl;
}

int main() {
	cin >> N >> M;
	rep(i, M) cin >> D[i + 1];
	solve();
	return 0;
}