#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

using Range = pair<int, int>;

void log_range_vector(const vector<Range>& ranges, const string& prefix = "") {
    clog << prefix;
    for (const Range& r : ranges) {
        clog << "(" << r.first << "," << r.second << ")" << " ";
    }
    clog << endl;
}

size_t get_min_ranges_amount(vector<Range> ranges, Range full_range) {
    sort(ranges.begin(), ranges.end());
    log_range_vector(ranges, "ranges: ");
    size_t i = 0, ans = 0;
    while (ranges[i].second < full_range.first) { i++; }
    int max_start = 0, current_end = ranges[i].second;
    while (true) {
        while (ranges[i].first <= max_start) {
            current_end = max(current_end, ranges[i].second);
            if (current_end >= full_range.second) { return ans + 1; }
            i++;
            if (i >= ranges.size()) { throw invalid_argument("No valid ranges found (inside loop)"); }
        }
        ans++;
        if (current_end >= full_range.second) { return ans; }
        max_start = current_end;
    }
    throw invalid_argument("No valid ranges found (outside loop)");
}

vector<Range> get_ranges(const vector<int>& monitors) {
    vector<Range> ranges;
    for (int i = 0; i < monitors.size(); i++) {
        ranges.emplace_back(i - monitors[i], i + monitors[i] + 1);
    }
    return ranges;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    size_t monitors_amount;
    cin >> monitors_amount;
    vector<int> monitors(monitors_amount);
    for (int i = 0; i < monitors_amount; i++) {
        cin >> monitors[i];
    }
    vector<Range> ranges = get_ranges(monitors);
    Range full_range = {0, monitors_amount};

    cout << get_min_ranges_amount(ranges, full_range) << endl;


    return 0;
}