const input = ['1,2,3,3,5'];

const gets = this.gets || ((arr, index) => () => arr[index++])(input, 0);
const print = this.print || console.log;

let arr = gets().split(',').map((e) => +e);
let indexes = arr.map((e, i) => i + 1);

let result = indexes.filter(x => !arr.includes(x)).join(',');

print(result);