usaco 1.3 barn repair...有意思...

/*
ID:chenjiong
PROG:barn1
LANG:C++
*/

#include <stdio.h>
#include <string.h>
#include <algorithm>

using namespace std;

const int MAXN = 205;

int M,S,C;
int p[MAXN];
int l[MAXN];

bool cmp(const int& x,const int& y)
{
return x > y;
}

int main()
{
freopen("barn1.in","r",stdin);
freopen("barn1.out","w",stdout);

int i;

scanf("%d%d%d",&M,&S,&C);
for (i = 0; i < C; i++)
scanf("%d",&p[i]);
sort(p,p + C);

for (i = 0; i < C - 1; i++)
l[i] = p[i + 1] - p[i] - 1;
sort(l,l + C - 1,cmp);

int sum = 0;
for (i = 0; i < M - 1; i++)
sum += l[i];

printf("%d\n",p[C - 1] - p[0] + 1 - sum);

return 0;
}