#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
#define DEBUG

int main()
{
    int a[10], s, ans;
    rep(i, 10)
        a[i] = i+1;
    rep(i, 10){
        cin >> s;
        a[s-1] = 0;
    }
    ans = 0;
    rep(i, 10)
        ans = max(a[i], ans);
    cout << ans << endl;
}