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1007.cpp
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1007.cpp
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#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define sort(a) sort((a).begin(), (a).end());
#define uniq(a) SORT(a);(a).erase(unique((a).begin(), (a).end()), (a).end());
#define find(a,x) find((a).begin(), (a).end(), (x)) != (a).end()
#define reverse(a) reverse((a).begin(), (a).end());
#define out(d) cout << (d);
#define outl(d) std::cout<<(d)<<"\n";
#define Yes() printf("Yes\n");
#define No() printf("No\n");
#define YES() printf("YES\n");
#define NO() printf("NO\n");
#define ceil(x, y) ((x + y - 1) / (y))
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
const ll MOD = 1000000007; // 10^9 + 7
int main() {
cin.tie(0);
ios::sync_with_stdio(false);
srand((unsigned)time(NULL));
ll n, k; cin >> n >> k;
vector<ll> a(n); rep(i, n) cin >> a[i];
if (a[k - 1] == 0) {
outl(0)
return 0;
}
ll lsum = 0, rsum = 0;
for (int i = k - 2; i >= 0; i--) {
lsum += a[i];
if (a[i] <= 1) break;
}
for (int i = k; i < n; i++) {
rsum += a[i];
if (a[i] <= 1) break;
}
if (a[k - 1] == 1) {
outl(max(lsum, rsum) + 1)
} else {
outl(lsum + rsum + a[k - 1])
}
}