#include <bits/stdc++.h>
using namespace std;
const int DIM = 1000005;
int arr[DIM];
pair<int, int> sgt[DIM * 4];
pair<int, int> updateNode(pair<int, int> p1, pair<int, int> p2) {
if (p1.first > p2.first)
return p1;
else
return p2;
}
void build(int nd, int le, int ri) {
if (le == ri)
sgt[nd] = make_pair(arr[le], le);
else {
int md = (le + ri) / 2;
build(nd * 2, le, md);
build(nd * 2 + 1, md + 1, ri);
sgt[nd] = updateNode(sgt[nd * 2], sgt[nd * 2 + 1]);
}
}
void update(int nd, int le, int ri, int ps, int vl) {
if (le == ri)
sgt[nd] = make_pair(vl, le);
else {
int md = (le + ri) / 2;
if (ps <= md)
update(nd * 2, le, md, ps, vl);
else
update(nd * 2 + 1, md + 1, ri, ps, vl);
sgt[nd] = updateNode(sgt[nd * 2], sgt[nd * 2 + 1]);
}
}
pair<int, int> query(int nd, int le, int ri, int st, int en) {
if (en < le || ri < st)
return make_pair(-1, -1);
if (st <= le && ri <= en)
return sgt[nd];
else {
int md = (le + ri) / 2;
return updateNode(query(nd * 2, le, md, st, en),
query(nd * 2 + 1, md + 1, ri, st, en));
}
}
int main(void) {
// freopen("c.in", "r", stdin);
// freopen("c.out", "w", stdout);
int n;
cin >> n;
for (int i = 1; i <= n; ++i)
cin >> arr[i];
build(1, 1, n);
int ans = 0;
while (sgt[1].first != 0) {
int h = sgt[1].first, p = 1;
++ans;
while (true) {
if (p > n)
break;
pair<int, int> pr = query(1, 1, n, p, n);
if (pr.first != h)
break;
update(1, 1, n, pr.second, 0);
p = pr.second + 1;
--h;
}
}
cout << ans;
return 0;
}
