#include <iostream>
#include <vector>
#include <algorithm>
#include <assert.h>
#include <map>
using namespace std;
int N,K;
vector<int> c, d;
map<int,int> dp;
int best(int max_sum){
if (dp.count(max_sum) > 0) return dp[max_sum];
//assert(max_sum >= 0);
//cout << max_sum << endl;
if (max_sum == 0) return 0;
int i = (upper_bound(c.begin(), c.end(), max_sum) - c.begin()) - 1;
if (d[i] == 1) return dp[max_sum] = best(c[i] - 1);
return dp[max_sum] = max(best(c[i] - 1), 1 + best(min(c[i] - 1, max_sum - c[i])));
}
int main(){
cin >> N >> K;
c.assign(N, 0);
d.assign(N, 0);
for (int i=0;i<N;i++) cin >> c[i] >> d[i];
cout << best(K-1) << endl;
cout << -1 << endl;
return 0;
}
