#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define F first
#define S second
const int N = 2e5 + 5, inf = 1e9 + 1, mod = 1e9 + 7;
int n, k, a[N], sum = 0;
vector < int > v;
void solve(){
cin >> n >> k;
for(int i = 1; i <= n; i++) cin >> a[i];
for(int i = 2; i <= n; i++) v.pb(a[i] - a[i - 1] - 1);
sort(v.begin(), v.end());
//for(auto to : v) cout << to << ' ';
int nn = v.size() - 1;
for(int i = nn; i > nn - k + 1; i--) sum += v[i];
cout << (a[n] - a[1] + 1) - sum << '\n';
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
//freopen("guard.in", "r", stdin);
//freopen("guard.out", "w", stdout);
int tt = 1;
//cin >> tt;
while(tt--) solve();
}
