#include<bits/stdc++.h>
using namespace std;
#define INIT ios_base :: sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define mp make_pair
#define pb push_back
#define ft first
#define sc second
#define ll long long
#define pii pair<int, int>
#define count_bits __builtin_popcount
#define int ll
/*ifstream fin("climbers.in");
#define cin fin
*/
int n,h[5010];
int d[5010][5010];
multiset<pair<int, pii>> ms;
bool vr[5010][5010];
bool btwn(int p1, int p2, int p3){
if(h[p3]>=h[p2]){
return (h[p1]>=h[p2] && h[p1]<=h[p3]);
}
else{
return (h[p1]>=h[p3] && h[p1]<=h[p2]);
}
}
void add_edge(int p, int l, int d0){
if( ((l>=n) || (p<=0))|| (vr[p][l]==true) || (!btwn(p, l, l+1)) || (l<=0) || (p>n) ){return;}
auto it=ms.find({d[p][l], {p, l} });
if(it!=ms.end()){if(d0<d[p][l] ){d[p][l]=d0;ms.erase(it); ms.insert({d[p][l], {p, l} }); } }
else{d[p][l]=d0;ms.insert({d[p][l], {p, l} }); }
}
void edges(int p, int l){
if( (h[p]==h[l]) ){
add_edge(p+1, l-1, d[p][l]+abs(h[p+1]-h[p]) );
add_edge(l-1, p, d[p][l]+abs(h[l-1]-h[p]));
add_edge(p-1, l-1, d[p][l]+abs(h[p-1]-h[p]));
add_edge(l-1, p-1, d[p][l]+abs(h[l-1]-h[p]));
}
if(h[p]==h[l+1]){
add_edge(p+1, l+1, d[p][l]+abs(h[p+1]-h[p]));
add_edge(l+2, p, d[p][l]+abs(h[l+2]-h[p]));
add_edge(p-1, l+1, d[p][l]+abs(h[p-1]-h[p]));
add_edge(l+2, p-1, d[p][l]+abs(h[l+2]-h[p]));
}
if(p==l){
add_edge(p-1, l, d[p][l]+abs(h[p-1]-h[p]));
add_edge(l+1, p-1, d[p][l]+abs(h[l+1]-h[p]));
return;
}
add_edge(p+1, l, d[p][l]+abs(h[p+1]-h[p]));
add_edge(l+1, p, d[p][l]+abs(h[l+1]-h[p]));
add_edge(l, p, d[p][l]+abs(h[l]-h[p]));
add_edge(p-1, l, d[p][l]+abs(h[p-1]-h[p]));
add_edge(l+1, p-1, d[p][l]+abs(h[l+1]-h[p]));
add_edge(l, p-1, d[p][l]+abs(h[l]-h[p]));
}
int32_t main(){
INIT
cin>>n;
for(int i=1; i<=n; i++){
cin>>h[i];
for(int j=1; j<=n;j++){
d[i][j]=-1;
}
}
int res=((int)1e17);
//cout<<res<<"\n"<<flush;
d[n][1]=0;
ms.insert({0, {n, 1} } );
while(!ms.empty()){
auto f=*ms.begin(); ms.erase(ms.begin());
int x=f.sc.ft, y=f.sc.sc;
d[x][y]=f.ft;
if(x==y){
cout<<d[x][y]<<"\n"; return 0;
}
vr[x][y]=true;
edges(x, y);
}
for(int i=1; i<=n; i++){
if(d[i][i]!=(-1) ){
res=min(res, d[i][i]);
}
}
if(res==((int)1e17) ){cout<<"-1"; return 0;}
cout<<res;
return 0;
}
