#include<bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define ii pair<ll,ll>
#define iii pair<ii,ll>
#define pb push_back
using namespace std;
const ll N=1e5+9;
const ll mod=1e9+7;
ll n,k,a[N],b[N],i;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cin>>n>>k;
for(i=1;i<=n;i++) cin>>a[i];
ll res=a[n]-a[1]+1;
for(i=2;i<=n;i++) {b[i-1]=a[i]-a[i-1]-1;}
sort(b+1,b+n,greater<ll>());
for(i=1;i<k;i++)
res-=b[i];
cout<<res;
}
/*
4 2
1 2 3 4 5 6 7 8
*/
