#include <bits/stdc++.h>

using namespace std;

int main() { int n, s = 0, a;

cin >> n;
for (int i = 1; i <= n; i++) {
	s = s + i;
}
for (int i = 1; i < n; i++) {
	cin >> a;
	s = s - a;
}
cout << s;

return 0;

}

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

int main() { long long n, a, b; cin >> n; b = (1 + n) * n / 2; for (int i = 1; i < n; i++) { cin >> a; b -= a; } cout << b; return 0; }