C++ :

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

#define int long long

int n, m, k;

signed main() {
    cin >> n >> m >> k;
    m -= n;
    int l = 0, r = m;
    while (l < r) {
        int mid = (l + r + 1) >> 1;
        int t1 = max((int)0, mid - (k - 1));
        int t2 = max((int)0, mid - (n - k));
        int s = (t1 + mid) * (mid - t1 + 1) / 2 + (t2 + mid) * (mid - t2 + 1) / 2 - mid;
        if (s > m)
            r = mid - 1;
        else
            l = mid;
    }
    cout << l + 1 << endl;
    return 0;
}