Javascript increment operator

Javascript increment operator

totalvalue = 0;
for (x=1; x<6; x++)
{
totalvalue += document.getElementById("rcv_amount_"+x).value;
}
rcv_amount_1 = 2 rcv_amount_2 = 4 rcv_amount_3 = 6
expected result is 12, but i am getting 0246.
Any help?