#include <iostream>

using namespace std;

int main()
{
    int n;
    cin>>n;
    int pos[n],val[n];
    for(int i=0; i<n; i++)
        cin>>pos[i]>>val[i];
        
    int freq[200001]= {};
    
    for(int i=0; i<n; i++)
    {
        if(freq[val[i]]==0)freq[val[i]]=pos[i];
        else if(freq[val[i]]>pos[i])
        {
            cout<<"NO";
            return 0;
        }
        else freq[val[i]]=pos[i];
    }
    cout<<"YES";
    return 0;
}

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MgowIDEKLTEgMQ==

2
0 1
-1 1