module Main;

import BinaryHeap;
import BoolArray;
import CPLib.Arithmetic;
import CPLib.DSegtree;
import CPLib.Graph;
import CPLib.IO;
import CPLib.LDSegtree;
import CPLib.UnionFind;
import CPLib.ZP;
import HashMap;
import HashSet;

type Z = ZP P1000000007;

main : IO () = (
    let cN = *read_i;
    let cS = *read_i;
    let cK = *read_i;
    let cX = cS - (cN*(cN-1))/2*cK;    
    if cX < 0 { 0.to_string.println };
    let dp = fill(cN + 1, fill(cX + 1, zp(0) : Z));
    let dp = dp[0][0].iset(zp(1));
    let dp = range(1, cN+1).fold(dp, |n, dp|
        range(0, cX+1).fold(dp, |x, dp|
            let c = cN - (n - 1);
            let v = if x >= c {
                dp[n-1][x].iget + dp[n][x-c].iget
            } else {
                dp[n-1][x].iget
            };
            dp[n][x].iset(v)
            // dp[n][x] = dp[n-1][x] + dp[n-1][x-c] + dp[n-1][x-2c] + ... 
            // = dp[n-1][x] + dp[n][x-c] if x >= c,
            // = dp[n-1][x]
        )
    );
    dp[cN][cX].iget.@value.to_string.println
);