Only R(German the best)

#include <vector>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <string>
#include <cmath>
using namespace std;
int main()
{
    int n, i, j, k, i1, p; cin >> n;
    vector<vector<int>> a(n, vector<int>(n));
    i = 0;
    j = 0;
    p = 0;
    k = 0;
    a[i][j] = 1;
    while (n > 0) {
        for (i1 = 0; i1 < n - 1; i1++) {
            j++;
            a[i][j] = 1;
            k++;
        }
        n -= p;
        for (i1 = 0; i1 < n - 1; i1++) {
            i++;
            a[i][j] = 1;
            k++;
        }
        for (i1 = 0; i1 < n - 1; i1++) {
            j--;
            a[i][j] = 1;
            k++;
        }
        n -= 2;
        p = 2;
        for (i1 = 0; i1 < n - 1; i1++) {
            i--;
            a[i][j] = 1;
            k++;
        }
    }
    for (i = 0; i < a.size(); i++) {
        for (j = 0; j < a[i].size(); j++)
            cout << a[i][j];
        cout << endl;
    }
    return 0;