#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<algorithm>
#include<vector>
#include<math.h>
#include<stack>
#include <typeinfo>  
using namespace std;
int main(void){
    vector<int> v; int s;
    for(int i = 0; i < 10; i++){
        cin >> s;
        v.push_back(s);
    }
    sort(v.begin(), v.end());
    int cnt = 1, ans = 0;
    for(int i = 0; i < 10; i++){
        if(v[i] == cnt){
            cnt++;
        }else{
            ans = cnt;
            break;
        }
    }
    cout << ans << endl;
    return 0;
}