I test it on random big integers and it work,
but i get WA#6 What's wrong?
I am sure, My program always gives right answer.

#include <stdio.h>

class ML  // my long integer
....

ML sqrt(ML x)
{
    ML l(1);
    ML r=x;
    ML m;
    ML E(1);
    while (l+E!=r)
    {
        m=(l+r)/2;
        if (m*m>x) r=m; else l=m;
    }
    return l;
}

int main()
{
    ML a;
    a.read();
    sqrt(a*2).write();
    return 0;
}