#include <bits/stdc++.h>
typedef long long ll;
typedef unsigned long long ull;
#define F first
#define S second
#define pb push_back
#define pq priority_queue
#define pl pair<ll,ll>
using namespace std;
constexpr int debug = 0;
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
pq<ll> inter;
ll n, match; cin >> n >> match;
vector<ll> cur;
match--;
for(int i = 0; i < n; i++){
ll a1; cin >> a1;
if(i > 0) inter.push(a1-cur.back()-1);
cur.pb(a1);
}
ll entire = cur.back() - cur[0] + 1;
//cout << entire << endl;
while((match > 0) && (!inter.empty())){
entire -= inter.top();
inter.pop();
match--;
//cout << entire << '\n';
}
cout << entire;
return 0;
}
