const int led1 = 13;
const int led2 = 12;
const int led3 = 11;
const int led4 = 10;
When you don't think about the length of your variables and just use int you mess up your code.
When you start numbering at 1 you mess up your code.
When you start copy / paste lines of codes you duplicate your mess up.
When you start numbering variables you have finally messed up your code.
Use ARRAYS.
Arrays start numbering with 0.