[HELP] : Can someone help me find the bug

I am getting MLE for the question: https://codeforces.com/contest/1855/problem/C1 (one of the recent div2 contests)

submission link : https://codeforces.com/contest/1855/submission/217028542

The approach that I am trying:
1. To increase the positive element greater than 20
2. make the index-1 greater than 0 with the help of max value index. (0 based indexing)
3. now increase the values incrementally

I am getting problem for the case, where there is a positive number present in the array ( I know this because if I assert the size, I get the runtime error )

snippet where the code gives problem

    else{
        ll mxidx = max_element(all(v)) - v.begin();
        // 1. increasing the max element
        while(v[mxidx] < 20) {
            ans.pb(mp(mxidx, mxidx));
            v[mxidx] += v[mxidx];
        }

        // 2. making the 2nd element greater than the 1st one
        while(v[0] > v[1]) {
            ans.pb(mp(1, mxidx));
            v[1] += v[mxidx];
        }

        // 3. incrementally increasing the values for the rest
        loop(i, 2, n) {
            while(v[i-1] > v[i]) {
                if(v[i-1] == 0) {               // to handle cases like [-1, -20, -1, 20]
                    ans.pb(mp(i, mxidx));
                    v[i] += v[mxidx];
                    continue;
                }
                //assert(sz(ans) <= 50);
                ans.pb(mp(i, i-1)) ;
                v[i] += v[i-1];
            }
        }
    }