#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int64_t oo = 1e18;
#define int long long
#define float long double
#define quickly ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define FOR(I, L, R) for(int I(L) ; I <= (int)R ; ++I)
#define FOD(I, R, L) for(int I(R) ; I >= (int)L ; --I)
#define FOA(I, A) for(auto &I : A)
#define print(A,L,R) FOR(OK, L, R){if(A[OK]<=-oo||A[OK]>=oo)cout<<"- ";else cout<<A[OK]<<' ';}cout<<'\n';
#define prints(A) FOA(OK, A){cout<<OK<<' ';}cout << '\n';
#define printz(A,L,R) FOR(OK, 1, L){FOR(KO, 1, R){if(A[OK][KO]>-oo&&A[OK][KO]<oo)cout<<A[OK][KO]<<' ';else cout << "- ";} cout << '\n';}cout << '\n';
#define fs first
#define sd second
#define se second.fs
#define th second.second
#define ii pair<int,int>
#define iii pair<int, ii>
#define all(A) A.begin(), A.end()
#define pow kjasdf
#define div dlfjsadh
const int N = 2e5 + 5;
const int mod = 1e9 + 7;
int n, k;
int a[N], b[N];
signed main(){ quickly
cin >> n >> k;
a[0] = -1;
FOR(i, 1, n){
cin >> a[i];
}
FOR(i, 1, n - 1){
b[i] = a[i + 1] - a[i] - 1;
}
sort(b + 1, b + n, greater<int>());
k--;
int ans = 0;
FOR(i, 1, k){
ans += b[i];
}
cout << a[n] - a[1] + 1 - ans;
}
