page 89 1 chapter (90 problem 20)

#include<bits/stdc++.h>

using namespace std;


#define Line cout << endl << "-------------------------------------------\n\n"
#define forn(i, n) for(int i = 0; i < int(n);i++)
const int INF = 1e9 + 13;
const int N = 1e5 + 13;


int main(){
    int n; cin >> n;
    vector<int> a(n);
    forn(i, n)
        cin >> a[i];
    for(vector<int>::iterator it = a.begin(); it != a.end(); it++)
        {
            vector<int>::iterator tmp = it;
            iter_swap(it++, ++tmp);
        }
    forn(i, n)
        cout << a[i] << ' ';
}