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

int main()
{
    long long int  i,j,k,s;
    double a,b,c,d;
    scanf("%lld %lld %lld %lld",&i,&j,&k,&s);
    if(s>=0)
    {
        d=sqrt(s);
        printf("%.4f\n",d);
    }
    if(k>=0)
    {
        c=sqrt(k);
        printf("%.4f\n",c);
    }
    if(j>=0)
    {
        b=sqrt(j);
        printf("%.4f\n",b);
    }

    if(i>=0)
    {
        a=sqrt(i);
        printf("%.4f\n",a);
    }



    return 0;
}

Why do you think there are only four numbers in input? Why do you think a number can be negative?

If you are new to OJ system...
The point is, the system will input any case that satisfies its question, not only the sample input.
Therefore, there might not be only 4 numbers for you to consider. It may input 100 numbers, which your code obviously cannot give the correct output.