#include <cstdio>

int main() {
  char c = 0;
  int a = 0;
  while(c != '\n') {
    c = std::getc(stdin);
    if(c == 'a') ++a;
  }
  for(int i = -1; i < a; ++i) {
    std::putc('a', stdout);
  }
  std::putc('\n', stdout);
}