#include<iostream>
#include<algorithm>
#include<vector>
#include<cmath>
#include<string>
using namespace std;
int main(){
    int N,M,K,ans=0;
    cin >> N >> M >> K;
    vector<int> a(N+1);
    for(int i=0;i<=N;i++){
           cin >> a[i];
           if(i!=0&&a[i]>a[i-1])  K+=M*(a[i]-a[i-1]);
    }
    cout << K << endl;
}