#include <bits/stdc++.h>
#define FOR(i,s,e) for(int i=(s);i<(int)(e);i++)
#define FOE(i,s,e) for(int i=(s);i<=(int)(e);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(x) (x).begin(), (x).end()
#define CLR(s) memset(s,0,sizeof(s))
#define PB push_back
#define x first
#define y second
using namespace std;
typedef long long LL;
typedef pair<int,int> pii;
typedef pair<LL, LL> pll;
typedef map<int,int> mii;
typedef vector<int> vi;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int N, K; cin >> N >> K;
vi A(N); REP(i, N) cin >> A[i];
vi D(N - 1); REP(i, N - 1) D[i] = A[i + 1] - A[i];
sort(ALL(D));
LL Ans = accumulate(begin(D), next(begin(D), N - K), K);
cout << Ans << endl;
return 0;
}
