const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;
void (async function () {
const input = (await readline()).split("");
let arr = [];
while (input.length >= 0) {
let i = 1;
while (i < input.length) {
if (input[i] == "0" && input[i - 1] == "0") {
const silce = input.splice(0, i);
arr.push(silce);
break;
}
i++;
}
if (i == input.length) {
arr.push(input);
break;
}
}
const ans = [];
arr = arr
.filter((val) => val.length > 1)
.filter((val) => isVal(val))
.sort((a, b) => b.length - a.length);
if (arr.length == 0) return console.log(-1);
console.log(arr[0].join(""));
})();
const isVal = (arr) => {
for (let i = 1; i < arr.length; i++) {
if (arr[i] == arr[i - 1]) return false;
}
return true;
};