#include <bits/stdc++.h>

int main()
{
        int n, m, k;
        std::cin >> n >> m >> k;

        std::vector<int> v;
        for(int i = 0; i < n; ++i)
        {
                int a;
                std::cin >> a;
                v.push_back(std::move(a));
        }

        --m;
        int dist = -1;
        for(int i = 0; i < v.size(); ++i)
        {
                if(v[i] == 0)
                {
                        continue;
                }
                else if(v[i] <= k)
                {
                        if(dist == -1)
                        {
                                dist = abs(i - m) * 10;
                        }
                        else
                        {
                                dist = std::min(dist, abs(i - m) * 10);
                        }
                }
        }

        std::cout << dist << '\n';
}