#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> PII;
const int N = 110;
int a[N];
int st[N];
int n;
void bfs() {
    queue<PII> q; // first:当前木桩号   sencond:从起点走了几步到达了当前的木桩
    q.push({1, 0});
    st[1] = 1;
    while (q.size()) {
        auto t = q.front();
        q.pop();
        if (t.first == n) {
            cout << t.second << endl;
            exit(0);
        }
        for (int i = 1; i <= a[t.first]; i++) {
            int x = t.first + i;
            if (st[x]) continue;
            q.push({x, t.second + 1});
            st[x] = 1;
        }
    }
}

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> a[i];
    bfs();
    return 0;
}