#include <bits/stdc++.h>
using namespace std;
#pragma warning(disable : 4996)
const long double PI = acosl(-1.0);
const long long MOD = 1e9 + 7;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
vector<long long> a;
long long solve(int l, int r) {
  if (l == r) return min(a[l], 1LL);
  long long temp = INT32_MAX;
  for (int i = l; i <= r; i++) temp = min(temp, a[i]);
  long long fv = r - l + 1;
  vector<int> pos;
  pos.push_back(l - 1);
  for (int i = l; i <= r; i++) {
    if (!a[i]) fv--;
    a[i] -= temp;
    if (a[i] == 0) {
      pos.push_back(i);
    }
  }
  pos.push_back(r + 1);
  for (int i = 1; i < pos.size(); i++) {
    if (pos[i - 1] + 1 != pos[i]) {
      temp += solve(pos[i - 1] + 1, pos[i] - 1);
    }
  }
  return min(temp, fv);
}
int main() {
  srand(time(0));
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  a.resize(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  cout << solve(0, n - 1);
}
