#include<bits/stdc++.h>
#define il inline
#define LL long long
#define db double
#define _(d) while(d(isdigit(ch=getchar())))
using namespace std;
const int N=1e6+5;
int n,a[N],q[N],l,r;LL f[N];
il int read(){
int x,f=1;char ch;
_(!)ch=='-'?f=-1:f;x=ch^48;
_()x=(x<<1)+(x<<3)+(ch^48);
return f*x;
}
il LL Y(int x){
return 2ll*f[x]+1ll*x*x+(LL)x;
}
il db K(int a,int b){
return (db)(Y(a)-Y(b))/(db)(a-b);
}
int main()
{
n=read();
for(int i=1;i<=n;i++)a[i]=read();
for(int i=1;i<=n;i++){
while(l<r&&K(q[l],q[l+1])<2*i)l++;
int j=q[l];
f[i]=f[j]+1ll*(i-j)*(i-j-1)/2ll+(LL)a[i];
while(l<r&&K(i,q[r])<=K(q[r-1],q[r]))r--;
q[++r]=i;
}
printf("%lld
",f[n]);
return 0;
}