#include <bits/stdc++.h>
#define rep(i, l, r) for (int i = (l); i < (r); i++)
using namespace std;

typedef long long ll;

int main() {
    int N, D;
    cin >> N >> D;
    vector<int> P(N), Q(N);
    vector<pair<int, int>> A, B;
    rep(i, 0, N) {
        cin >> P[i] >> Q[i];
        if (P[i] < Q[i]) A.push_back(make_pair(P[i], Q[i]));
        else B.push_back(make_pair(P[i], Q[i]));
    }
    sort(A.begin(), A.end());
    sort(B.begin(), B.end());
    ll ans = 0, x = 0;
    rep(i, 0, A.size()) {
        x -= A[i].first;
        ans = min(ans, x);
        x += A[i].second;
    }
    for (int i = B.size() - 1; i >= 0; i--) {
        x -= B[i].first;
        ans = min(ans, x);
        x += B[i].second;
    }
    cout << ans << endl;
}