#include <iostream>
using namespace std;

void solve()
{
    int n; //碗数量
    cin >> n;
    int* container = new int[n + 1]; //存储米饭粒数的容器
    for (int i = 0; i < n + 1; i++)
        container[i] = i; //对容器赋值,第n个碗装了n粒米

    //将输入数据排除(置0)
    int temp;
    for (int i = 0; i < n - 1; i++)
    {
        cin >> temp;
        container[temp] = 0;
    }

    //遍历容器,不为0的就是拿走的碗里的米饭数量
    for (int i = 1; i < n; i++)
        if (container[i] != 0)
            cout << container[i];
}

int main()
{
    solve();
}