import java.io.PrintWriter;

import java.util.*;

public class Main {

    static long cal(long a1,long d,long n){

        a1=Math.max(a1, 1); //至少有一个。

        long k=Math.min(n,a1); //k个构成等差序列

        return k*a1+k*(k-1)/2*d+(n-k);  //等差序列求和+剩余都为1

    }

    static long check(long val,long k,long n){

        return cal(val-1,-1,k-1)+cal(val-1,-1,n-k)+val; //左边+右边+自己

    }

    public static void main(String[] args) {

        Scanner cin = new Scanner(System.in);

        PrintWriter out = new PrintWriter(System.out);

        long n=cin.nextLong(),m=cin.nextLong(),k=cin.nextLong();

        long L=1,R=(m-(n-1)),mid;

        while(R>=L){ //二分。

            mid=(L+R)/2;

            if(check(mid,k,n)>m){

                R=mid-1;

            }else{

                L=mid+1;

            }

        }

        out.println(R);

        cin.close();

        out.flush();

    }

}