#include <iostream>

using namespace std;

int getMissing(int* array)
{
	int i = 0;
	while(1)
	{
		if(!array[i++])
		{
			return i;
		}
	}
}

int main()
{
	int n, m, o;
	while(cin >> n)
	{
		int* array = new int[n];
		m = 0;
		for(int i = 0; i < n; i++)
		{
			array[i]=0;
		}
		while((++m) != n)
		{
			cin >> o;
			array[o-1] = o;
		}
		cout << getMissing(array) << endl;
		delete[] array;
	}
	return 0;
}