#include <bits/stdc++.h>
using namespace std;
int main() {
freopen("B.in", "r", stdin);
freopen("B.out", "w", stdout);
int n, num[10000], index = 0, maxSize = 0;
stack stk;
cin >> n;
for (int i = 0; i < n; i++) cin >> num[i];
for (int i = 0; i < n; i++) {
stk.push(i + 1);
maxSize = max(maxSize, (int)stk.size());
while (!stk.empty() && stk.top() == num[index]) {
stk.pop();
index++;
}
}
if (stk.empty()) {
cout << "yes\n" << maxSize;
} else {
cout << "no";
}
return 0; }