int main(){
	int n,x,y,i;         //?????n?x?y????i?j???i??j???0?i,j<n?i?????
	cin>>n;
	int a[n];
	for(i=0;i<n;i++)     //a[n]?????????????0
		a[i]=0;
	while(true){         //???
		cin>>x>>y;
		if(x==0&&y==0) break;     //?????0????
		a[y]=a[y]+x;              //????????
	}
	for(i=0;i<n;i++)     //??a[n]
		if(a[i]==n*(n-1)/2-i){    //??????????
			cout<<i;
			return 0;
		}
	cout<<"NOT FIUND";
	return 0;
}