#include <bits/stdc++.h>
using namespace std;
const int INF = 1234567890;
vector<int> v;
struct node {
int s, e, m, val, lazy;
node *l, *r;
node (int S, int E) :
s(S), e(E), m((S+E)/2), val(0), lazy(0) {
if (s != e) {
l = new node(s, m);
r = new node(m+1, e);
}
}
void prop() {
l->val += lazy;
l->lazy += lazy;
r->val += lazy;
r->lazy += lazy;
lazy = 0;
}
void up(int x, int y, int k) {
if (x <= s && e <= y) {
val += k;
lazy += k;
return;
}
else if (x > e || y < s) return;
prop();
l->up(x, y, k);
r->up(x, y, k);
//if (l->s == l->e && l->val == 0) v.push_back(l->s);
//if (r->s == r->e && r->val == 0) v.push_back(r->s);
val = min(l->val, r->val);
}
int q(int x, int y) {
if (x <= s && e <= y) return val;
else if (x > e || y < s) return INF;
prop();
return min(l->q(x, y), r->q(x, y));
}
int bsta(int x) {
if (s == e) {
if (val == 0) return s;
else return INF;
}
prop();
if (x <= m && l->val == 0) {
if (l->bsta(x) != INF) return l->bsta(x);
}
if (r->val == 0) {
return r->bsta(x);
}
else return INF;
}
}*tree;
int main() {
int n;
cin >> n;
set<int> nz;
tree = new node(0, n-1);
int arr[n];
for (int i = 0; i < n; i++) {
cin >> arr[i];
if (arr[i] != 0) {
nz.insert(i);}
tree->up(i, i, arr[i]);}
set<int>::iterator it;
int ans = 0;
while (nz.begin() != nz.end()) {
int temp = tree->bsta(*(nz.begin()));
int temp2 = tree->q(*(nz.begin()), temp-1);
tree->up(*(nz.begin()), temp-1, 0-temp2);
ans++;
for (int i = 0; i < n; i++) if (tree->q(i, i) == 0 && nz.find(i) != nz.end()) nz.erase(nz.find(i));
}
cout << ans;
return 0;
}
