uses crt;
var v,r:text;
i,n,t,j,t2,max:integer;
a:array[1..100] of integer;
begin
assign(v,'HEALTH.inp');
reset(v);
readln(v,n);
assign(r,'HEALTH.out');
rewrite(r);
for i:=1 to n do readln(a[i]);
for i:=1 to n do
begin
t:=0;
for j:=i+1 to n do
 if a[i]=a[j] then t:=1;
if t<>1 then
 if max<a[i] then begin max:=a[i];t2:=i;end;
end;
if t2<>0 then write(r,t2) else write(r,'-1'); 
close(r);
end.

uses crt;
var n,i,j,tg,count: integer;
    a,b: array[1..100000] of integer;
    fi,fo: text;
begin
    assign(fi,'HEALTH.INP'); reset(fi);
    assign(fo,'HEALTH.OUT'); rewrite(fo);
    readln(fi,n);
    count:=0;
    for i:=1 to n do read(fi,a[i]);
    for i:=1 to n do begin
        tg:=1;
        if (a[i]<>a[i-1]) and (a[i]<>a[i+1]) then begin
            for j:=i+1 to n do if a[i]=a[j] then tg:=0;
            if tg=1 then begin
                count:=count+1;
                b[count]:=i;
            end;
        end;
    end;
    if (count=0) then write(fo,-1) else begin
        for i:=2 to count do if b[1]>b[i] then b[1]:=b[i];
        write(fo,b[1]);
    end;
    close(fi);
    close(fo);
end.