unsigned char unknown (unsigned char num){
unsigned char resu =0;
unsigned char msk =0b00001000 ;

while ( msk > 0){
resu = resu | msk ;
if( resu * resu > num ){
resu = resu ^ msk ;
}

msk = msk >>1;
}
return resu ;

}


int main( int argc, const char* argv[] ){

printf("%d", unknown(123));

}