import java.io.*;
import java.util.*;

public class E2 implements Runnable{
	public static void main (String[] args) {new Thread(null, new E2(), "_cf", 1 << 28).start();}

	public void run() {
		DeoxysS fs = new DeoxysS();
		PrintWriter out = new PrintWriter(System.out);
		System.err.println("Go!");

		int k = fs.nextInt();
		int n = fs.nextInt();
		int[] a = fs.nextIntArray(n); sort(a);
		int[] diffs = new int[n - 1];
		for(int i = 0; i < n - 1; i++) diffs[i] = a[i + 1] - a[i];
		Index[] b = new Index[n - 1];
		for(int i = 0; i < n - 1; i++) b[i] = new Index(i, diffs[i]);
		Arrays.sort(b, (x, y) -> Integer.compare(x.val, y.val));
		b = Arrays.copyOfRange(b, 0, Math.min(b.length, 3 * k + 100));
		Arrays.sort(b, (x, y) -> Integer.compare(x.idx, y.idx));

		long[] dp = new long[b.length + 2];
		long oo = (long)1e15;
		for(int ii = 0; ii < k; ii++) {
			long[] ndp = new long[dp.length]; Arrays.fill(ndp, oo);
			for(int i = b.length - 1; i >= 0; i--) {
				ndp[i] = Math.min(dp[i + 2] + b[i].val, ndp[i + 1]);
				if(i + 1 < b.length && b[i+1].idx-b[i].idx > 1) ndp[i] = Math.min(ndp[i], dp[i+1] + b[i].val);
			}
			dp = ndp;
		}
		out.println(dp[0]);
		
		out.close();
	}

	class Index {
		int idx, val;
		Index(int a, int b) { idx = a; val = b; }
		public String toString() { return "Idx " + idx + " Val " + val; }
	}

	void sort (int[] a) {
		int n = a.length;
		for(int i = 0; i < 50; i++) {
			Random r = new Random();
			int x = r.nextInt(n), y = r.nextInt(n);
			int temp = a[x];
			a[x] = a[y];
			a[y] = temp;
		}
		Arrays.sort(a);
	}

	class DeoxysS {
		public int BS = 1<<16;
		public char NC = (char)0;
		byte[] buf = new byte[BS];
		int bId = 0, size = 0;
		char c = NC;
		double num = 1;
		BufferedInputStream in;

		public DeoxysS() {
			in = new BufferedInputStream(System.in, BS);
		}

		public DeoxysS(String s) throws FileNotFoundException {
			in = new BufferedInputStream(new FileInputStream(new File(s)), BS);
		}

		public char nextChar(){
			while(bId==size) {
				try {
					size = in.read(buf);
				}catch(Exception e) {
					return NC;
				}                
				if(size==-1)return NC;
				bId=0;
			}
			return (char)buf[bId++];
		}

		public int nextInt() {
			return (int)nextLong();
		}

		public long nextLong() {
			num=1;
			boolean neg = false;
			if(c==NC)c=nextChar();
			for(;(c<'0' || c>'9'); c = nextChar()) {
				if(c=='-')neg=true;
			}
			long res = 0;
			for(; c>='0' && c <='9'; c=nextChar()) {
				res = (res<<3)+(res<<1)+c-'0';
				num*=10;
			}
			return neg?-res:res;
		}

		public double nextDouble() {
			double cur = nextLong();
			return c!='.' ? cur:cur+nextLong()/num;
		}

		public String next() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c>32) {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}

		public String nextLine() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c!='\n') {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}

		public boolean hasNext() {
			if(c>32)return true;
			while(true) {
				c=nextChar();
				if(c==NC)return false;
				else if(c>32)return true;
			}
		}
		
		public int[] nextIntArray(int n) {
			int[] res = new int[n];
			for(int i = 0; i < n; i++) res[i] = nextInt();
			return res;
		}
		
	}

}