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function tong(a,b){
    while(a.length<b.length) a="0"+a;
    while (a.length >b.length) b = "0" + b;
    a="0"+a;
    b="0"+b;
    var du=0;
    var c="";
    for(var i=a.length-1;i>=0;i--){
        c=((Number(a[i])+Number(b[i])+du)%10).toString()+c;
        du = Math.floor((Number(a[i]) + Number(b[i]) + du) / 10);
    }
    while(c[0]==="0") c=c.substring(1); 
    return c;
}
function hieu(a,b){
    while (a.length > b.length) b = "0" + b;
    while (a.length < b.length) a = "0" + a;
    a = "0" + a;
    b = "0" + b;
    var c="";
    if(a<b){ var t=a; a=b;b=t;}
    var no=0;
    for(var i=a.length-1;i>=0;i--)
        {
            if((Number(a[i])-no)<Number(b[i])){
                c = (Number(a[i]) - no + 10 - Number(b[i])).toString()+c;
                no = 1;
            } else {
                c = (Number(a[i]) - no - Number(b[i])).toString() + c;
                no=0;
            }
        }
    while (c[0] === "0") c = c.substring(1); 
    if(c==="") c=0;
    return c;
}
function tich(a,b){
    var p=[];
    while (a.length > b.length) b = "0" + b;
    while (a.length < b.length) a = "0" + a;
    if (a < b) { var t = a; a = b; b = t; }
    a = "0" + a; m=a.length;
    b = "0" + b; n=b.length; 
    for(var i=n-1;i>=0;i--){
        var c="";
        var nho=0;
        for(var j=m-1;j>=0;j--){
            c=((Number(a[j])*Number(b[i])+nho)%10).toString()+c;
            nho=Math.floor((Number(a[j])*Number(b[i])+nho)/10);
        }
        p[n-i-1]=c;
    }
    dem="0";
    for(var i=1;i<n;i++){
        p[i]=p[i]+dem;
        dem=dem+"0";
    }
    var result="0";
    for(var i=0;i<n;i++) result=tong(result,p[i]);
    return result;
}
var a = "13456"; var b = "986";
console.log("tong la ",tong(a, b));
console.log("hieu la ",hieu(a,b));
console.log("tich la ",tich(a,b));