CF1041E

#include<bits/stdc++.h>

using namespace std;

#define gc c=getchar()
#define r(x) read(x)
#define ll long long

template<typename T>
inline void read(T&x){
    x=0;T k=1;char gc;
    while(!isdigit(c)){if(c=='-')k=-1;gc;}
    while(isdigit(c)){x=x*10+c-'0';gc;}x*=k;
}

const int N=1e3+7;

int a[N];
int ans[N];
bool vis[N];

int main(){
    // freopen(".in","r",stdin);
    // freopen(".out","w",stdout);
    int n;r(n);
    for(int i=1;i<n;++i){
        int u,v;r(u),r(v);
        if(u!=n && v!=n)return puts("NO"),0;
        if(u==v)return puts("NO"),0;
        if(u==n)swap(u,v);
        a[i]=u;
    }
    sort(a+1,a+n);
    for(int i=1;i<n;++i){
        if(a[i]<i)return puts("NO"),0;
    }
    for(int i=1;i<n;++i){
        if(a[i]!=a[i-1])ans[i]=a[i],vis[a[i]]=1;
        else {
            for(int j=1;j<=a[i];++j){
                if(!vis[j]){
                    ans[i]=j;
                    vis[j]=1;
                    break;
                }
            }
        }
    }
    puts("YES");
    ans[n]=n;
    for(int i=1;i<n;++i){
        printf("%d %d\n",ans[i],ans[i+1]);
    }
    return 0;
}