#include<bits/stdc++.h>
#define int long long
using namespace std;
#define fi first
#define se second
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define eb emplace_back
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef unsigned long long ull;
 
long long read() {
    long long res=0, w=1; char c=getchar();
    while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
    while(isdigit(c)) {res=res*10+c-48, c=getchar();}
    return res*w;
}

const int N=1e5+9;
int n,k,a[N],b[N],ans;

signed main() {
    n=read(), k=read();
    rep(i,1,n) a[i]=read();
    rep(i,1,n-1) b[i]=a[i+1]-a[i]-1;
    ans=a[n];
    sort(b+1,b+n,greater<int>());
    rep(i,1,k-1) ans-=b[i];
    printf("%lld\n",ans);
    return 0;
}