#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
using pear=pair<ll, ll>;
#define v vector
#define fi first
#define se second
#define nl << '\n'
#define uk << ' '
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
// freopen(".inp","r",stdin);
// freopen(".out","w",stdout);
cin.exceptions(cin.failbit);
ll n, k;
cin >> n >> k;
ll i;
vector<ll> a(n), gap;
for(i=0; i<n; i++){
cin >> a[i];
}
for(i=1; i<n; i++){
gap.push_back(a[i]-a[i-1]);
}
sort(gap.rbegin(), gap.rend());
ll ans=a[n-1]-a[0]+1;
for(i=0; i<k-1; i++){
ans-=gap[i]-1;
}
cout << ans;
}
