Merkkijono

#include <iostream>
#include <string>
 
int main() {
	std::string jono;
	std::cin >> jono;
	jono += '\n';
	for (std::string::size_type i = 0; jono[i] != '\n';) {
		auto j = jono.find_first_not_of(jono[i], i);
		if (j - i > 1) {
			jono.erase(i, j - i);
			if (i > 0) {
				--i;
			}
		} else {
			++i;
		}
	}
	std::cout << jono;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED