Language: C++

#include <bits/stdc++.h>

#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(25)<< fixed<<p<<endl;
int dx_ori[4] = { -1,0, 1,0 }, dy_ori[4] = { 0,1,0,-1 };
int dx[4] = {0, 0, 0, 0}, dy[4] = {0, 0, 0, 0};
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
const ll MOD = 1000000007;
//const ll MOD = 998244353;
// #define mp make_pair
//#define endl '\n'


ll gcd(ll a, ll b) {
  if (b > a) {
    swap(a, b);
  }
  ll r = a%b;
  while (r != 0) {
    a = b;
    b = r;
    r = a%b;
  }
  return b;
}

ll lcm(ll a, ll b) {
  return (a / gcd(a, b))*b;
}



signed main() {
  int a, b;
  cin >> a >> b;
  rep1 (i, 3) {
    if (a != i and b != i) {
      cout << i << endl;
      return 0;
    }
  }
  int n;
  cin >> n;
  vi a(n);
  rep (i, n) cin >> a[i];

  int now = 1;
  int ans = 0;
  rep (i, n) {
    if (a[i] == now) now++;
    else ans++;
  }
  if (ans == n) {
    cout << -1 << endl;
  }
  else {
    cout << ans << endl;
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:83:6: error: conflicting declaration 'std::vector<long long int> a'
   83 |   vi a(n);
      |      ^
a.cc:73:7: note: previous declaration as 'll a'
   73 |   int a, b;
      |       ^
a.cc:84:22: error: invalid types 'll {aka long long int}[ll {aka long long int}]' for array subscript
   84 |   rep (i, n) cin >> a[i];
      |                      ^
a.cc:89:10: error: invalid types 'll {aka long long int}[ll {aka long long int}]' for array subscript
   89 |     if (a[i] == now) now++;
      |          ^