#include <iostream>
#include <vector>
#include <optional>
int main() {
std::vector<std::optional<int>> vec;
vec.push_back(10);
vec.push_back(std::nullopt);
vec.push_back(15);
for (auto i : vec) {
if (*i) {
std::cout << *i << std::endl;
} else {
std::cout << "value is not exist\n";
}
}
return 0;
}