Revise paste Untitled

#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <set>
using namespace std;

int main()
{
    int n;
    cin >> n;
    
    vector<int> v(n);
    set<pair<int, int>> st;
    int sum = 0;
    for(int i = 0; i < n; i++) {
        cin >> v[i];
        st.insert(make_pair(v[i], i));
        sum += v[i] - 1;
    }
    if(sum >= n) {
        cout << "PROBLEM" << endl;
        return 0;
    }
    
    for(int i = 0; i < n; i++) {
        set<pair<int, int> >::iterator F = st.begin();
        set<pair<int, int> >::iterator L = st.end();
        L--;
        
        if(F->first > 0 and L->first > 0 and L->second != F->second) {
            cout << F->second + 1 << " " << L->second + 1 << endl;
            pair<int, int> p1 = *F;
            pair<int, int> p2 = *L;
            st.erase(F);
            st.erase(L);
            if(p1.first > 1) {
                st.insert(make_pair(p1.first - 1, p1.second));
            }
            if(p2.first > 1) {
                st.insert(make_pair(p2.first - 1, p2.second));
            }
        }
        
    }

return 0;
}