const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;
void (async function () {
const arr = (await readline()).split(",").map(Number);
const k = Number(await readline());
const map = new Map();
let res = Infinity;
for (let i = 0; i < arr.length; i++) {
if (map.has(arr[i])) {
const left = map.get(arr[i]);
if (i - left <= k) {
res = Math.min(res, left);
}
}
map.set(arr[i], i);
}
console.log(res === Infinity ? -1 : res);
})();