#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<to;x++)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N;
int A[101];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	y=0;
	FOR(i,N) cin>>A[i],y+=A[i];
	
	int mi=10000000;
	for(j=1;j<=200;j++) {
		if(j*j>y) continue;
		int tot=0;
		FOR(i,N) {
			if(i<j) x=i+1;
			else x=max(0,j*2-i-1);
			if(A[i]>x) tot+=A[i]-x;
		}
		mi=min(mi,tot);
	}
	cout << mi << endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false);
	FOR(i,argc-1) s+=argv[i+1],s+='\n';
	FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	solve(); return 0;
}