#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000000

int main(){
	
	int N;
	cin>>N;
	vector<int> B(N);
	
	vector<int> ind(0);
	
	for(int i=0;i<N;i++){
		cin>>B[i];
		if(B[i]>1)ind.push_back(i);
	}
	
	reverse(ind.begin(),ind.end());
	
	long long ans = 0;
	
	for(int i=0;i<N;i++){
		if(B[i]!=0)continue;
		
		B[i] = 1;
		int j = ind.back();
		ans += (long long)abs(j-i);
		B[j]--;
		if(B[j]==1)ind.pop_back();
		
	}
	
	cout<<ans<<endl;
	
	
	
	return 0;
	
}