#include <cstdio>
#include <algorithm>
#include <set>

using namespace std;

int n, a;
int niz[5001];
set<int> dani;
set<int> jel;

int main( void ){
        
    scanf( "%d", &n );
    for( int i = 0; i < n; ++i ){
         scanf( "%d", &niz[i] );
         dani.insert( niz[i] );
    }
    
    int period = 0; int k = 1;
    
    jel.insert( 1 );
    
    for( int i = 1; i < n; ++i ){
         period = niz[i] - 1;
         k = 1;
         while( ( 1 + period * k ) <= niz[n-1] ){
                if( dani.count( 1 + period * k ) > 0 ) jel.insert( 1 + period * k );
                ++k;
         }
         if( jel.size() == n ) { printf( "%d\n", i ); return 0; }
    }
    
    printf( "%d\n", n );
    
    return 0;
}