#include <bits/stdc++.h>
using namespace std;
using ull = uint64_t;
using ll = int64_t;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define N4(f)	\
	f(0,1)	\
	f(0,-1)	\
	f(1,0)	\
	f(-1,0)
#define N8(f)	\
	f(y+1,x+1)	\
	f(y+1,x+0)	\
	f(y+1,x-1)	\
	f(y+0,x+1)	\
	f(y+0,x-1)	\
	f(y-1,x+1)	\
	f(y-1,x+0)	\
	f(y-1,x-1)
#define N9(f)	\
	f(y+1,x+1)	\
	f(y+1,x+0)	\
	f(y+1,x-1)	\
	f(y+0,x+1)	\
	f(y+0,x+0)	\
	f(y+0,x-1)	\
	f(y-1,x+1)	\
	f(y-1,x+0)	\
	f(y-1,x-1)

signed main() {
	int n,k,x;cin>>n>>k>>x;
	ll ans=0;
	ll anssum=0;
	ll csum=0;
	multiset<int> v;
	rep(i,k-1)v.insert(0);
	int a;cin>>a;ans=a-x;
	anssum=x;
	csum=x;
	v.insert(a);
	rep(i,n-1) {
		csum+=x;
		int a;cin>>a;
		auto el=v.begin();
		if (a-*el>csum-anssum) {
			// cout<<ans<<","<<a<<","<<*el<<","<<csum<<","<<anssum<<","<<endl;
			ans+=a-*el-csum+anssum;
			anssum=csum;
			v.erase(el);
			v.insert(a);
		}
	}
	cout<<ans<<endl;
}