【USACO 1.3】Barn Repair

/*******************************************
  TASK: barn1
  LANG: C++ 
  Created Time: 2016/9/9 14:36:17
 *********************************/

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int a[201],d[201];
int main(){
	freopen("barn1.in","r",stdin);
	freopen("barn1.out","w",stdout);
	int m,s,c;
	cin>>m>>s>>c;
	for(int i=0;i<c;i++)cin>>a[i];
	sort(a,a+c);
	int ans=a[c-1]-a[0]+1;
	for(int i=1;i<c;i++)
		d[i]=a[i]-a[i-1]-1;		
	sort(d+1,d+c);
	for(int i=1;i<min(m,c);i++)
		ans-=d[c-i];
	cout<<ans<<endl;
	
}