#include <iostream>
using namespace std;

int main(){
    int arr[9];
    int arr_compare[10];
    for (int i=0;i<9;i++){
        cin>>arr[i];
    }
    int missID=-1;
    for (int i=0;i<9;i++){
        if(arr[i]!=arr_compare[i]){
            missID=i;
            break;
        }
    }
    cout<<missID<<endl;
}