#include<bits/stdc++.h>
using namespace std;
deque<int>a;
int n,s,x,i;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)
		cin>>x,a.push_front(x);
	while(!a.empty())
	{
		i++;
		int flag=0,minn;
		for(int j=0;j<a.size();j++)
		    minn=min(minn,a[j]);
		if(i==a.size())i=minn;
		for(int j=0;j<a.size();j++)
			if(a[j]>a.size()){flag=1;break;}
		if(flag==1)break;
		if(a.back()==i)s+=a.back(),a.pop_back(),i=minn;
		else a.push_front(a.back()),a.pop_back(),i++;
	}	
	cout<<s;
    return 0;
}