#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char& s) {
  string res = "'";
  res += s;
  res += "'";
  return res;
}
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (i) res += ", ";
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
vector<long long> a;
long long solve(long long l, long long r) {
  if (l > r) return 0;
  long long mn = *min_element(a.begin() + l, a.begin() + r + 1);
  if (mn == 0) {
    long long res = 0, pr = -1;
    for (long long i = l; i <= r; i++) {
      if (a[i] == 0) {
        if (pr != -1) res += solve(pr, i - 1);
        pr = -1;
      } else {
        if (pr == -1) pr = i;
      }
    }
    if (pr != -1) res += solve(pr, r);
    return res;
  }
  long long res = r - l + 1;
  for (long long i = l; i <= r; i++) a[i] -= mn;
  res = min(res, solve(l, r) + mn);
  for (long long i = l; i <= r; i++) a[i] += mn;
  return res;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  a.resize(n);
  for (long long i = 0; i < n; i++) cin >> a[i];
  cout << solve(0, n - 1);
}
