#include <bits/stdc++.h>
using namespace std;
typedef long long int64;

int main()
{
  int N, A[100000], ret;

  cin >> N;
  for(int i = 0; i < N; i++) {
    cin >> A[i];
  }
  
  bool f = true;
  int prev = 0;
  while(N > 0 && A[N - 1] == N) --N;
  for(int i = 1; i < N; i++) {
    if(A[i] < A[0]) continue;
    if(prev > A[i]) f = false;
    prev = A[i];
  }
  
  if(!f) cout << N - 1<< endl;
  else cout << A[0] - 1 << endl;
}