/*
* Author : shora
*/
#include <bits/stdc++.h>
#define print(_v) for (auto &_ : _v) {cerr << _ << ' ';} cerr << endl;
using namespace std;
using ll = long long;
const int oo = 1e9;
const int N = 1e5;
int a[N], b[N-1];
int n, k;
int main() {
cin.tie(0)->sync_with_stdio(0); cout.tie(0);
cin >> n >> k;
for (int i = 0; i < n; ++i)
cin >> a[i];
for (int i = 0; i < n-1; ++i)
b[i] = a[i] - a[i+1] + 1;
sort(b, b + n - 1);
ll res = a[n-1]-a[0]+1;
// a[n-1]-a[0]+1 => a[n-1]-a[m+1]+1 + a[m]-a[0]+1 = a[n-1]-a[0]+1 + a[m]-a[m+1]+1
for (int i = 0; i < k-1; ++i)
res += b[i];
cout << res;
return 0;
}
