#include <string>
#include <vector>

using namespace std;

std::string DNAStrand(const std::string& dna){
  std::vector<std::string> DNA;
  for (int i = 0; i < dna.length(); i++)
    DNA.push_back(dna);
  uint_fast32_t i=0;
  for (auto elements : DNA){
    if(elements == "A"){
        DNA.assign( i, "T");
        i++;
        break;
    }
    else if(elements == "T"){
        DNA.assign( i, "A");
        i++;
        break;
    } 
    else if(elements == "C"){
        DNA.assign( i, "G");
        i++;
        break;
    } 
    else if(elements == "G"){
        DNA.assign( i, "C");
        i++;
    } 
  }
  std::string str(DNA.begin(), DNA.end());
}