#include<iostream> using namespace std;

int a[100001]; int main(){ int n,m,a1; cin>>n>>m; for(int i=1;i<=m;i++){ cin>>a1; a[a1] = 1; } for (int i = 1;i<=n;i++){ if(a[i]==0){ cout<<i<<endl; }

}
return 0;

}