// I ♡ 鞠婧祎
// #pragma GCC optimize("Ofast")
// #pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
#define freopen(name) if(fopen(name".INP","r")) {freopen (name".INP","r",stdin); freopen (name".OUT","w",stdout);}
using namespace std;
using ll = long long;
void justDoIt();
int main() {
// freopen("");
ios_base::sync_with_stdio(false);
cin.tie(0);
justDoIt();
return 0;
}
const int N = 1e5 + 5;
int a[N];
void test() {
int n, k;
cin >> n >> k;
ll sum = 0;
vector<int> v;
for (int i = 1; i <= n; i++) {
cin >> a[i];
if (i >= 2) {
v.push_back(a[i] - a[i - 1] - 1);
}
}
sum = a[n] + 1 - a[1];
sort(v.begin(), v.end(), greater<int>());
for (int i = 0; i < k - 1; i++) {
sum -= v[i];
}
cout << sum;
}
void justDoIt() {
int t = 1;
// cin >> t;
for (int tests = 1; tests <= t; tests++) {
test();
}
}
