/*#include <bits/stdc++.h>
using namespace std;
int x[107], f[107][107];
int main() {
	int n;
	cin >> n;
	for (int i = 1; i <= n; ++i) {                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
	}
	for (int i = 1; i <= n; ++i) {
		for (int j = 0; j <= i*i; ++j) {
			if (j >= x[i]) {
				f[i][j] = max(f[i - 1][j], f[i - 1][j - x[i]] + x[i]);
			} else {
				f[i][j] = f[i - 1][j];
			}
		}
	}
	cout << f[n][x[n]];
}*/
#include <bits/stdc++.h>
using namespace std;
int x[100007];
int main() {
	int n;
	int ans = 0, ct = 0, ct2 = 0;
	cin >> n;
	for (int i = 1; i <= n; ++i) {
		cin >> x[i];
	}
	for (int i = 1; i <= n; ++i) {
		if (x[i] >= x[i - 1]) {
		ct += x[i];
			ct += x[i - 1] % i;
			return 0;
		} else {
	    ct2 += x[i - 1];
			ct2 += x[i] % i;
		}
	}
	ans = max(ct, ct2);
	cout << ans;
}