#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    long long L;
    cin >> n >> L;

    vector<long long> h(n + 1), w(n + 1);
    for (int i = 1; i <= n; ++i) {
        cin >> h[i] >> w[i];
    }

    const long long INF = 4e18;
    vector<long long> dp(n + 1, INF);
    dp[0] = 0;

    for (int i = 1; i <= n; ++i) {
        long long maxh = 0, sumw = 0;
        // 枚举最后一层的左端点 j（第 j..i 本书在同一层）
        for (int j = i; j >= 1; --j) {
            sumw += w[j];
            if (sumw > L) break;
            maxh = max(maxh, h[j]);
            dp[i] = min(dp[i], dp[j - 1] + maxh);
        }
    }

    cout << dp[n] << '\n';
    return 0;
}