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

let word = gets();
let arrayOfSymbols = [];
let biggestSeries = 1;
let currentSeries = 1;
let symbol = '';


let output = '';

for(let i = 0; i < word.length; i ++){
    arrayOfSymbols.push(word[i]);
}

for(let i = 0; i < arrayOfSymbols.length-1; i++){
    if(arrayOfSymbols[i]===arrayOfSymbols[i+1]){
        currentSeries++;
        if(currentSeries>biggestSeries){
            biggestSeries = currentSeries;
            symbol = arrayOfSymbols[i];
        }
    }else{
        currentSeries =1;
    }
}

if(biggestSeries === 1){
    symbol+=word[0];
}

for(let i = 0; i < biggestSeries; i++){
    output+=symbol;
}


print(output);