7.2.19

#include <iostream>
#include <string>

using namespace std;

int main() {
    string in, out;
    int lenght, i, j;

    setlocale(LC_ALL, "Russian");

    cout << "Введите строку: ";
    getline(cin, in);
    lenght = in.length();
    out = in;

    for (i = 1, j = 0; i < lenght; i += 2, j++)
        out[j] = in[i];

    for (i = 0, j = lenght-1; i < lenght; i += 2, j--)
        out[j] = in[i];

    cout << out;
}