#include <bits/stdc++.h>
using namespace std;
long long n, a[5005], ans;
long long solve(long long l, long long r) {
  if (l > r) return 0;
  if (l == r) return a[l] != 0;
  long long minn = 1 << 30, p = l;
  for (register long long i = l; i <= r; ++i) minn = min(minn, a[i]);
  for (register long long i = l; i <= r; ++i) a[i] -= minn;
  long long sum = minn;
  if (sum > r - l + 1) return r - l + 1;
  for (register long long i = l; i <= r; ++i)
    if (!a[i]) {
      sum += solve(p, i - 1);
      p = i + 1;
      if (sum > r - l + 1) return r - l + 1;
    }
  sum += solve(p, r);
  return min(sum, r - l + 1);
}
signed main() {
  scanf("%lld", &n);
  for (register long long i = 1; i <= n; ++i) scanf("%lld", &a[i]);
  printf("%lld\n", solve(1, n));
  return 0;
}
