#include<bits/stdc++.h>
using namespace std; 
int n,bs,zh,zh2;
int main()
{
    cin>>n;
    for (int i=1;i<n;i++)
    {
        cin>>bs;
        zh+=bs;
        zh2+=i;
    }
    zh2+=n;
    cout<<zh2-zh;
    return 0;
}