C++ :

#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int main()
{
	double a,x0,x1;
	cin>>a;
	x0=a/2;
	x1=(x0+a/x0)/2;
	while (fabs(x1-x0)>1e-5)
	{
		x0=x1;
		x1=(x0+a/x0)/2;
	}
	printf("%.3lf\n",x1);
	return 0;
}

Pascal :

var s:longint;
begin
  readln(s);
  writeln(sqrt(s):0:3);
end.