注释特别详细包懂的题解

import java.util.*;
public class twic {
    static long cou(long t) {
        long res=0;
        while(t>0) {
            t/=5;
            res+=t;
        }
        return res;
    }
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        long n=sc.nextLong(),num=1;
        long l=0,r=Long.MAX_VALUE,mid;
        while(l<=r) {
            mid=(l+r)/2;
            if(cou(mid)<n) {
                l=mid+1;
            }
            else {
                r=mid-1;
            }
        }
        if(cou(l)==n)System.out.println(l);
        else System.out.println(-1);
    }
}