#include <bits/stdc++.h>
using namespace std;
#ifdef DEBUG
#include "../Library/debug.h"
#else
#define dbg(x...)
// #define cin fin
// #define cout fout
// const string FILE_NAME = ""; ifstream fin(FILE_NAME + ".in"); ofstream fout(FILE_NAME + ".out");
#endif
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) for (int i = 0; i < (a); ++i)
#define FORd(i, a, b) for (int i = (b) - 1; i >= (a); --i)
#define F0Rd(i, a) for (int i = (a) - 1; i >= 0; --i)
#define trav(a, x) for (auto& a : x)
#define f first
#define s second
#define pb push_back
#define sz(x) (int)(x).size()
#define all(x) x.begin(), x.end()
const char nl = '\n';
const int INF = 1e9;
const int MOD = 1e9 + 7;
void solve(){
int n, k;
cin >> n >> k;
vi a(n), b;
F0R(i, n){
cin >> a[i];
if(i > 0){
b.pb(a[i] - a[i - 1]);
}
}
sort(all(b), greater<int>());
ll ans = 0;
F0R(i, k - 1){
ans += b[i] - 1;
}
cout << a[n - 1] - a[0] + 1 - ans << nl;
}
int32_t main(){
ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int TC = 1;
// cin >> TC;
while(TC--){
solve();
}
return 0;
}
