#include <iostream>
#include <string>
using namespace std;

string longestZero(string);

int main(){
    string sequence;

    do{
        cout<< "Enter binary sequence (q/Q to quit)";
        getline(cin,sequence);

        if(sequence == "q" || sequence == "Q") break;   //user wants to quit

        cout<< "\tLongest sequence: "<< longestZero(sequence)<< endl;

    } while (sequence != "q" && sequence != "Q");

    return 0;
}

string longestZero(string seq){
    string longest= "";
    int rep= 0, i= 0, highest;

    while(i<seq.size()){
        if(seq.at(i) == '0'){   //count zeros
            if(++rep>highest) highest= rep;
        }

        if(seq.at(i) == '1') rep= 0;    //reset counter

        ++i;
    }
    longest.insert(0, highest, '0');
    return longest;
}