#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define st first
#define nd second
#define pb push_back
#define ins insert
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pdd pair<double, double>
#define t3 tuple<int, int, int>
#define t4 tuple<int, int, int, int>
#define chmn(a, b) a=min(a, b)
#define chmx(a, b) a=max(a, b)
#define For(i, a, b) for(int i=(int)a; i<=(int)b; i++)
#define Forx(i, a, b, x) for(int i=(int)a; i<=(int)b; i+=(int)x)
#define F0r(i, n) for(int i=0; i<(int)n; i++)
#define Rof(i, a, b) for(int i=(int)a; i>=(int)b; i--)
#define R0f(i, n) for(int i=(int)(n-1); i>=(int)0; i--)
#define rep(n) F0r(_, (int)n)
#define all(v) (v).begin(), (v).end()
const int N = 1e5+5;
using ll = long long;
using namespace std;
int a[N];
void solve(){
int n, k;
cin >> n >> k;
vector<int> v;
For(i, 1, n){
cin >> a[i];
if(i>1)v.pb(a[i]-a[i-1]-1);
}
sort(all(v), greater<int>());
int ans=a[n]-a[1]+1, id=0;
rep(k-1){
ans-=v[id++];
}
cout << ans;
}
int32_t main(){
ios_base::sync_with_stdio(false); cin.tie(0);
int Tcases=1;
//cin >> Tcases;
while(Tcases--)solve();
return 0;
}
