Timus-1654. Cipher Message

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <stack>
//#include <unordered_set>
//#include <unordered_map>
#include <queue>
//#include <ctime>
//#include <cassert>
//#include <complex>
#include <string>
#include <cstring>
//#include <chrono>
//#include <random>
#include <bitset>
using namespace std;
//using namespace chrono;
#define pb push_back
#define FastIO ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define F first
#define S second
typedef long long ll;
typedef vector< int > vi;
typedef vector< ll > V;
typedef map<int, int > mp;
#define debug cout << -1 << endl;
#define REP(i, a, b) for(int i=a; i<b; i++)
#define f0r(i, n) for (int i = 0; i < n; ++i)
#define fore(a, x) for (auto& a : x)
#define fori(i, a, b) for (int i = (a); i < (b); ++i)
//#define pop pop_back
#define sz(a) (int)a.size()
//#define fin cin
//#define fout cout
const ll MOD = 1000000007;
const int INF = (int)1e9;
int dx[] = {-1, 0, 1, -1, 1, -1, 0, 1};
int dy[] = {-1, -1, -1, 0, 0, 1, 1, 1};
const double PI = acos(-1.0);
const double diff = 1e-6;


void solve()
{
	//FastIO;
	//freopen("mowing.in","r",stdin);
	//freopen("mowing.out","w",stdout);
	string str;
	cin >> str;
	int n = str.size();
	stack< char > s;
	for(int i=0; i<n; i++) {
		if(!s.empty()) {
			if(s.top()==str[i]) {
				s.pop();
				continue;
			}
		}
		s.push(str[i]);
	}
	string ans;
	while(!s.empty()) {
		ans += s.top();
		s.pop();
	}
	reverse(ans.begin(), ans.end());
	cout << ans << "\n";
}

int main()
{
    int t;
    t = 1;
    //cin >> t;
    while(t--) {
		solve();
	}
}