#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("lipsa.in");
ofstream fout("lipsa.out");
int n,x,s,sg,i;
int main()
{
fin>>n;//cate numere citim
i=1;
while(i<=n-1)
{
fin>>x;//citim primul numar
s=s+x;//la suma adaugam numaru citit
i++;
}
sg=n*(n+1)/2;//formula pentru suma gausiana
fout<<sg-s;
fout.close();
return 0;
}
