#include <bits/stdc++.h>
using namespace std;
#define int int64_t
#define f0(i, n) for(int32_t i = 0; i < (n); i++)
#define f1(i, n) for(int32_t i = 1; i <= (n); i++)
#define inp(x) int x; cin >> x
#define inp2(a, b) int a, b; cin >> a >> b
void solve1() {
inp2(n, k);
int T[n];
f0(i, n) {
cin >> T[i];
}
vector<int> gaps;
f0(i, n-1) {
gaps.push_back(T[i+1] - T[i]-1);
}
sort(gaps.begin(), gaps.end(), greater<int>());
int ans = T[n-1] + 1 - T[0];
f0(i, k - 1) {
ans -= gaps[i];
}
cout << ans << endl;
}
int32_t main() {
#if __has_include("LOCAL.hh")
#include "LOCAL.hh"
#endif
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#else
ios_base::sync_with_stdio(0);
cin.tie(0);
#endif
solve1();
return 0;
}
