#include <bits/stdc++.h>
using namespace std;
int a[100001];
set<int> st;
int main() {
int n;
scanf("%d",&n);
for(int i=1;i<=2*n-1;i++)st.insert(i);
for(int i=0;i<n;i++){
scanf("%d",&a[i]);
if (i==0) {
printf("%d ",a[i]);
st.erase(a[i]);
}
else{
if (a[i]>a[i-1]) {
if (st.find(a[i])!=st.end()){
printf("%d %d ",a[i],*(--st.end()));
st.erase(a[i]);
st.erase(--st.end());
}
else{
printf("%d %d ",*(--(--st.end())),*(--st.end()));
st.erase(--(--st.end()));
st.erase(--st.end());
}
}
else if (a[i]==a[i-1]){
printf("%d %d ",*(st.begin()),*(--st.end()));
st.erase(st.begin());
st.erase(--st.end());
}
else{
if (st.find(a[i])!=st.end()){
printf("%d %d ",a[i],*(st.begin()));
st.erase(a[i]);
st.erase(st.begin());
}
else{
printf("%d %d ",*(++st.begin()),*(st.begin()));
st.erase(++(st.begin()));
st.erase(st.begin());
}
}
}
}
return 0;
}
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