#include<bits/stdc++.h> //:3
using namespace std;
typedef long long ll;
#define all(a) (a).begin(), (a).end()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define pi pair<int, int>
#define sz(x) (int)((x).size())
#define int long long
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
const ll inf = 2e9;
const ll mod = 1e9 + 7;
const int N = 2e5 + 11;
const int X = 1e6;
const ll INF64 = 3e18 + 1;
const double eps = 1e-14;
const double PI = acos(-1);
//ifstream in(".in");
//ofstream out(".out");
int n, k, a[N], dif[N];
void solve(){
cin >> n >> k;
for(int i = 1; i <= n; i++){
cin >> a[i];
}
int tot = a[n] - a[1] + 1;
if(k == 1){
cout << tot << '\n';
return;
}
for(int i = 1; i < n; i++){
dif[i] = a[i + 1] - a[i] - 1;
}
sort(dif + 1, dif + n);
reverse(dif + 1, dif + n);
int ans = inf, sum = 0;
for(int i = 1; i < k; i++){
sum += dif[i];
ans = min(ans, tot - sum);
}
cout << ans << '\n';
}
int32_t main(){
ios_base :: sync_with_stdio(0); cin.tie(0); cout.tie(0);
//cout << setprecision(6) << fixed;
int T = 1;
//cin >> T;
while(T--){
solve();
}
}
