#include "bits/stdc++.h"
#define _CRT_SECURE_NO_WARNINGS
#define rep(i,n) for(int i = 0;i < n;i++)
#define REP(i,n,k) for(int i = n;i < k;i++)
#define P(p) cout << (p) << endl;
#define sP(p) cout << setprecision(15) << fixed << p << endl;
#define Pi pair<int,int>
#define IINF 1e9
#define LINF 1e18
#define vi vector<int>
#define mp(a,b) make_pair(a,b)

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
int dx[] = { 1, -1 , 0 , 0};
int dy[] = { 0,  0,  1, -1};

unsigned long long str_to_int(std::string str) {
	unsigned long long ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

bool isPrime(int n) {
	if (n <= 1)return false;
	if (n == 2)return true;
	if (n % 2 == 0)return false;
	for (int i = 3; i*i <= n; i += 2) {
		if (n%i == 0)return false;
	}
	return true;
}

void solve() {
	int a;
	rep(i, 9) {
		cin >> a;
		if (i + 1 != a) {
			P(i + 1);
			return;
		}
	}
	P(10);
}

int main() {
	solve();
	return 0;
}