import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


long calc(long a, long b) {
  return (gcd(a, b) == 1) ? ((a - 1) * (b - 1)) : 0;
}

void main() {
  try {
    for (; ; ) {
      const N = readInt;
      auto A = new long[N];
      foreach (i; 0 .. N) {
        A[i] = readLong;
      }
      
      int[][2] iss;
      foreach (i; 0 .. N) {
        iss[A[i] & 1] ~= i;
      }
      
      long ans;
      alias Op = Tuple!(int, "x", int, "y");
      Op[] ops;
      void oper(int x, int y) {
        ops ~= Op(x, y);
      }
      if (iss[0].length >= 2) {
        oper(iss[0][0], iss[0][1]);
      } else if (iss[0].length >= 1 && iss[1].length >= 2) {
        oper(iss[1][0], iss[1][1]);
        int i = iss[0][0];
        if (iss[1][0] < iss[0][0]) --i;
        if (iss[1][1] < iss[0][0]) --i;
        oper(N - 2, i);
      } else if (iss[1].length >= 4) {
        oper(iss[1][2], iss[1][3]);
        oper(iss[1][0], iss[1][1]);
        oper(N - 4, N - 3);
      } else if (N == 2) {
        //
      } else if (N == 3) {
        ans = long.max;
        int sm;
        foreach (s; 0 .. 3) {
          const cost = calc(calc(A[s % 3], A[(s + 1) % 3]), A[(s + 2) % 3]);
          if (chmin(ans, cost)) {
            sm = s;
          }
        }
        oper(sm, (sm + 1) % 3);
      } else {
        assert(false);
      }
      for (; ops.length < N - 1; ) {
        oper(0, 1);
      }
      
      writeln(ans);
      foreach (op; ops) {
        writeln(op.x + 1, " ", op.y + 1);
      }
    }
  } catch (EOFException e) {
  }
}