#include<bits/stdc++.h>
/*
Created By Tornado2004
*/
using namespace std;
#define debug(x) cout << '[' << #x << " is: " << x << "] " << endl;
#define imod(a , n) (a % n + n ) % n
#define fastio ios_base::sync_with_stdio(false);cin.tie(0);
#define inF freopen("marathon.in","r",stdin );
#define outF freopen("marathon.out" , "w" , stdout ) ;
#define sor(v) sort(v.begin() , v.end());
#define print(v) for(auto f : v ) cout << f << " " ;
#define rsor(v) sort(v.rbegin() , v.rend());
#define rev(v) reverse(v.begin() , v.end());
#define scan(v)for(auto &it : v)cin >> it ;
#define ll long long
#define logar(x , y) log(x) / log(y)
#define int ll
#define pii pair<int , int >
const int N = 1e5 + 5 , K = 11 , M = N * 4 ;
const ll MOD = 1e9 + 7 , oo = 1e9 , OO = 1e18 , mod = MOD ;
const double pi = acos(-1) , eps = 1e-6 ;
//37
// (a ^ b / c ) % mod = (a ^ b ) % MOD * (c ^ (mod - 2)) % mod
// ريتني اعدم المود
int di[] = {-1 , -1 , -1 , -2 , -2 , -2 , 1 , 1 , 1 , 2 , 2 , 2};
int dj[] = {1 , -2 , 2 , -1 , 2 , 1 , -2 , -1 , 2 , -1 , -2 , 1};
int32_t main()
{ //inF;
// inF;outF;
fastio;
int n , k ;
cin >> n >> k ;
k -- ;
vector<int> v ;
int past , f ;
for(int i = 0 ; i < n; i ++){
int a ;
cin >> a ;
if(i == 0)f = a ;
if(i)v.push_back(a - past - 1);
past = a ;
}
int ans = past + 1 - f ;
sort(v.rbegin() , v.rend());
for(int i = 0 ; i < k ; i ++)
ans -= v[i];
cout << ans ;
}
/*🎂🎁🎉👑
HAPPY TORNADO`S BIRTHDAY 💜💜
*/
