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#include<bits/stdc++.h>
using namespace std;typedef long long LL;
const int N=1e6+10;int n;
LL a[N],s[N];int main()
{cin>>n;LL sum=0;for(int i=1;i<=n;i++){scanf("%lld",&a[i]);s[i]=s[i-1]+a[i];sum+=a[i];}LL del=0;for(LL d=0;d<=n-1;d++){LL t=d*(d+1);if(t>s[d+1]) del=max(del,t-s[d+1]);}sum=sum+del;cout<<sum;return 0;
}