#include <iostream>
#include <map>
using namespace std;
int main()
{
map<int, int>hash;
int n, m;
cin>>n; //Given range 1 to n
cin>>m; // size of array
for(int i=1;i<=m;i++)
{
int x;
cin>>x;
hash[x] = 1;
}
for(int i=1;i<=n;i++)
{
if(hash[i] == 0)
cout<<i<<endl;
}
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8bWFwPgp1c2luZyBuYW1lc3BhY2Ugc3RkOwoKaW50IG1haW4oKSAKewoJbWFwPGludCwgaW50Pmhhc2g7CglpbnQgbiwgbTsKCQoJY2luPj5uOwkJCS8vR2l2ZW4gcmFuZ2UgMSB0byBuCgljaW4+Pm07CQkJLy8gc2l6ZSBvZiBhcnJheQoJCglmb3IoaW50IGk9MTtpPD1tO2krKykKCXsKCQlpbnQgeDsKCQljaW4+Png7CgkJaGFzaFt4XSA9IDE7Cgl9CgkKCWZvcihpbnQgaT0xO2k8PW47aSsrKQoJewoJCWlmKGhhc2hbaV0gPT0gMCkKCQljb3V0PDxpPDxlbmRsOwoJfQoJcmV0dXJuIDA7Cn0=