#include <stdio.h>
#include <stdlib.h>


int main(void)
{
  int cleny;
  int d;
  int i;
  int* pole;

  scanf("%d",&cleny);
  pole=(int*) malloc(cleny*sizeof(int));
  if(cleny==EOF)
    return 0;

 for( i=0;i<cleny;i++)
  scanf("%d",&pole[i]);
 i--;
 d=pole[i]-pole[i-1];
 i--;
    while(i>0 && d+pole[i-1]==pole[i])
      i--;
      

    printf("%d\n",i+1);


 
  while(scanf("%d",&cleny))
{
  pole=(int*) realloc(pole,cleny*sizeof(int));
  if(cleny==EOF)
    break;

 for( i=0;i<cleny;i++)
  scanf("%d",&pole[i]);
 i--;
 d=pole[i]-pole[i-1];
 i--;
    while(i>0 && d+pole[i-1]==pole[i])
      i--;
      

    printf("%d\n",i+1);


 }
  free(pole);
  return 0;
}