#include <iostream>
#include <fstream>

using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");

int v[1005],x[1005];

int main()
{
    int gen,w,min=20000000,ok=0;
    f >>gen>>w;
    for(int i=0;i<=gen;i++){
        f >>v[i]>>x[i];
        if(v[i]==w){
            if(min>x[i]){
                min=x[i];
                ok=1;
            }
        }
    }
    if(ok==1)
        g <<min;
    else
        g <<"-1";

    return 0;
}