#include <iostream>
#include <algorithm>
using namespace std;

const int MAX_N = 200000;
int N, idx1, idx2;
int A[MAX_N];
bool ans, tmp;

int main() {
    cin >> N;
    for (int i = 0; i < N; i++)
        cin >> A[i];
    idx1 = 0; idx2 = N - 1;
    while (idx1 < N && A[idx1] <= idx1 + 1)
        idx1++;
    while (idx2 >= 0 && A[idx2] <= N - idx2)
        idx2--;
    if ((idx1 > idx2) || ((idx1 == idx2) && A[idx1] <= N))
        ans = true;
    cout << ((ans) ? "Yes" : "No") << endl;
    return 0;
}