#include <bits/stdc++.h>
using namespace std;
#define inf 0x3F3F3F3F
const int MXN = 3e3 + 5;
const int mod = 1e9 + 7;
void _()
{
int n, a, b;
cin >> n >> a >> b;
vector<int> dp(n + 1, 0), ndp;
dp[0] = 1;
for (int val = 0; val < n; val++)
{
ndp = vector<int>(n + 1, 0);
for (int c = 0; c <= n; c++)
{
if (!dp[c]) continue;
if (val == a || val == b)
{
if (c) ndp[c] = (ndp[c] + dp[c]) % mod;
ndp[c + 1] = (ndp[c + 1] + dp[c]) % mod;
}
else
{
int c1 = c + 1 - (a <= c) - (b <= c);
int c2 = 2 * c - (a <= c) - (b <= c);
ndp[c + 1] = (ndp[c + 1] + dp[c] * c1 % mod) % mod;
if (c > 0) ndp[c - 1] = (ndp[c - 1] + dp[c] * c2 % mod) % mod;
}
}
swap(ndp, dp);
}
cout << dp[1] << '\n';
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
while (t--) _();
}
