#include<bits/stdc++.h>
using namespace std;

#define step(i, s, n, d) for(int i=s; i<n; i+=d)
#define FOR(i,s,n) step(i,s,n,1)
#define rep(i,n) FOR(i,0,n)
#define gets(x) x; cin >> x;
#define puts(x) x; cout << x << endl;
#define list_input(x, n) x[n]; rep(i,n){ gets(x[i]);}
#define ll long long

int main(){
	int check;
	FOR(i, 1, 11){
		cin >> check;
		if (check != i){
			puts(i)
			exit(0);
		}
	}
}