function btn_value(main){
var d_value = document.getElementById('input_text').value;
var a_value = d_value+main;
document.getElementById('input_text').value = a_value;
}
function sum_value(){
var sum = document.getElementById('input_text').value;
var main_sum =eval(sum);
document.getElementById('input_text').value = main_sum;
}
function cler_main(){
document.getElementById('input_text').value = "";
}