#include <bits/stdc++.h> #include <ext/pb_ds/assoc_container.hpp> #include <ext/pb_ds/tree_policy.hpp> using ll = long long; using namespace std; using namespace __gnu_pbds; template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; const double pi = acos(-1); const int N = 2e3 + 5, K = 1e3 + 5, SQ = 500, M = 1e9 + 7; //#define TESTS //#define INTERACTIVE //#define COMMUNICATION /* * Remember who you are. */ void pre() { } int dp[N][N], vis[N][N], vid, n, s, e; int rec(int i, int j) { if (j < 0) return 0; if (i == n) return j == 1; auto &ret = dp[i][j], &v = vis[i][j]; if (v == vid) return ret; v = vid; ret = 0; if (s == i || e == i) ret = rec(i + 1, j + 1) + rec(i + 1, j); else ret = 1ll * rec(i + 1, j + 1) * (j + 1 - (i > s) - (i > e)) % M + 1ll * rec(i + 1, j - 1) * (j - 1) % M; return ret %= M; } void solve() { cin >> n >> s >> e; s--, e--; ++vid; cout << rec(0, 0); } void solve2() { } signed main() { ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr); #ifdef CAROOT #ifndef INTERACTIVE freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout); #endif #else #endif int tt = 1; pre(); #ifdef COMMUNICATION string run; cin >> run; #endif #ifdef TESTS cin >> tt; #endif for (int tc = 1; tc <= tt; ++tc) { #ifdef COMMUNICATION if (run == "first") solve(); else solve2(); #else solve(); #endif cout << '\n'; } }