#include <iostream>
#include <list>
#include <cassert>

int main() {
    std::list<int> const l { 1, 2, 3, 4 };
    const std::size_t index { 1 };
    assert(index < l.size());
    auto it = begin(l);
    std::advance(it, index);
    std::cout << (*it) << std::endl;
}