CodeForces 81A

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

const int MAXN = 300010;
char cat[MAXN];
string s;

int main()
{
    cin >> s;
    int cnt = 0;
    cat[cnt] = s[0];
    for(int i = 1; i < s.size(); i++){
        if(cat[cnt] == s[i]){
            if(!cnt) {
                cat[cnt] = s[i + 1];
                i++;
            }
            else  cnt--;
        }
        else cat[++cnt] = s[i];
    }
    cat[++cnt] = '\0';
    cout << cat << endl;
    return 0;
}