#include<bits/stdc++.h>
using namespace std;
using ll=long long;
const int N=2e5+5;
int n;
int h[N];
ll p;
ll f[N][2][2];
int main(){
    scanf("%d%lld",&n,&p);
    memset(f,0x3f,sizeof(f));
    for(int i=1;i<=n;++i){
        scanf("%d",&h[i]);
    }
    f[1][1][0]=0;
    f[1][1][1]=0;
    f[1][0][0]=0;
    f[1][0][1]=0;
    for(int i=2;i<=n;++i){
        f[i][1][0]=min(f[i-1][1][0]+min(p,1ll*max(0,h[i]-h[i-1])),f[i-1][1][1]+p);
        f[i][1][1]=min(f[i-1][0][0],f[i-1][0][1])+p+max(0,h[i-1]-h[i]);
        f[i][0][0]=min(f[i-1][1][0],f[i-1][1][1]);
        f[i][0][1]=min(f[i-1][0][1],f[i-1][0][0])+max(0,h[i-1]-h[i]);
    }
    cout<<min(f[n][1][0],f[n][1][1]);
    return 0;
}