C++ :

#include<bits/stdc++.h>
using namespace std;
int m,s,c;
int num[250];
int ch[250];
int main()
{
	//freopen("1.in","r",stdin);
	scanf("%d%d%d",&m,&s,&c);
	for(int i=1;i<=c;i++)
		scanf("%d",&num[i]);
	sort(num+1,num+1+c);
	int ans=num[c]-num[1]+1;
	for(int i=1;i<c;i++)
		ch[i]=num[i+1]-num[i]-1;
	sort(ch,ch+c);
	for(int i=c-1;i>=c-m+1;i--)
		ans-=ch[i];
	printf("%d",ans);
}

Pascal :

var a,b:array[0..201] of longint;
    ans,tot,n:integer;
procedure qsort(l,r:longint);
var i,j,x,t:longint;
begin
 i:=l; j:=r;
 x:=a[l+random(r-l)];
 repeat
  while a[i]>x do inc(i);
  while a[j]<x do dec(j);
  if i<=j then
  begin
   t:=a[i]; a[i]:=a[j]; a[j]:=t;
   inc(i); dec(j);
  end;
 until i>j;
 if i<r then qsort(i,r);
 if l<j then qsort(l,j);
end;

procedure init;
var i,min,max:longint;
begin
 readln(tot,n,n);
 min:=maxlongint; max:=-maxlongint;
 for i:=1 to n do
 begin
  readln(a[i]);
  if a[i]<min then min:=a[i];
  if a[i]>max then max:=a[i];
 end;
 ans:=max-min;
end;

procedure main;
var i:longint;
begin
 for i:=2 to n do b[i]:=abs(a[i]-a[i-1]);
 a:=b; qsort(2,n);
 if tot>=n then tot:=n;
 for i:=2 to 2+tot-2 do dec(ans,a[i]);
 writeln(ans+tot);
end;

begin
 randomize;
 init;
 qsort(1,n);
 main;
end.