how do i solve this

package com.codegym.task.task02.task0217;
/*
Minimum of four numbers
*/
public class Solution {
public static int min(int a, int b, int c, int d) {
//write your code here
int f = 0;
if ((a<=b) && (a<=c) && (a<=d))
{
f = a;
}
if ((b<=a) && (b<=c) && (b<=d))
{
f = b;
}
if ((c<=a) && (c<=b) && (c<=d))
{
f = c;
}
if ((d<=a) && (d<=b) &&(d<=c)){
f = d;
}
return f;
}
}
public static int min(int a, int b) {
/* int f = 0
if (a<=b){
f = a;
}
if (b<=a){
f = b;
}
return f; */
}
public static void main(String[] args) throws Exception {
System.out.println(min(-20, -10));
System.out.println(min(-20, -10, -30, -40));
System.out.println(min(-20, -10, -30, 40));
System.out.println(min(-40, -10, -30, 40));
}
}

"The function min(a, b, c, d) should use (call) the function min(a, b)"