#include <fstream>
#include <algorithm>

const unsigned int SIZE(10001 * 1001 + 1);
unsigned int v [SIZE];
typedef std::pair<unsigned int,unsigned int> generator;
generator gen [5001];

int main (void)
{
    unsigned int n,g;
    std::ifstream input("energii.in");
    input >> n >> g;
    generator *ptr(gen),*end(gen + n);
    do
    {
        input >> ptr->first >> ptr->second;
        ++ptr;
    }
    while (ptr < end);
    input.close();
    --ptr;
    unsigned int p,c;
    unsigned int *it,*limit(v + 5100);
    do
    {
        it = limit;
        p = ptr->first;
        c = ptr->second;
        do
        {
            if (*it && (it[p] > *it + c || !it[p]))
                it[p] = *it + c;
            --it;
        }
        while (it >= v);
        if (!v[p] || v[p] > c)
            v[p] = c;
        --ptr;
    }
    while (ptr >= gen);
    input.close();
    unsigned int result(-1);
    it = v + g - 1;
    do
    {
        if (*it && result > *it)
            result = *it;
        ++it;
    }
    while (it < limit);
    std::ofstream output("energii.out");
    if (result & (1 << 31))
        output << "-1";
    else
        output << result;
    output.put('\n');
    return 0;
}