Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	io := NewIo()
	defer io.Flush()
	for {
		N, K, S := io.NextInt(), io.NextInt(), io.NextInt()
		if N == 0 {
			break
		}
		dp := [21][11][156]int{}
		for i := 0; i <= N; i++ {
			dp[i][0][0] = 1
		}
		for i := 1; i <= N; i++ {
			for j := 1; j <= K; j++ {
				for k := 1; k <= S; k++ {
					if k-i >= 0 {
						dp[i][j][k] += dp[i-1][j-1][k-i]
					}
					dp[i][j][k] += dp[i-1][j][k]
				}
			}
		}
		io.Println(dp[N][K][S])
	}
}

// I/O template
type Io struct {
	reader    *bufio.Reader
	writer    *bufio.Writer
	tokens    []string
	nextToken int
}

func NewIo() *Io {
	return &Io{
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
	}
}

func (io *Io) Flush() {
	err := io.writer.Flush()
	if err != nil {
		panic(err)
	}
}

func (io *Io) NextLine() string {
	var buff []byte
	for {
		line, isPrefix, err := io.reader.ReadLine()
		if err != nil {
			panic(err)
		}
		buff = append(buff, line...)
		if !isPrefix {
			break
		}
	}
	return string(buff)
}

func (io *Io) Next() string {
	for io.nextToken >= len(io.tokens) {
		line := io.NextLine()
		io.tokens = strings.Fields(line)
		io.nextToken = 0
	}
	s := io.tokens[io.nextToken]
	io.nextToken++
	return s
}

func (io *Io) NextInt() int {
	i, err := strconv.Atoi(io.Next())
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) NextFloat() float64 {
	i, err := strconv.ParseFloat(io.Next(), 64)
	if err != nil {
		panic(err)
	}
	return i
}

func (io *Io) Println(a ...interface{}) {
	fmt.Fprintln(io.writer, a...)
}

func (io *Io) Printf(format string, a ...interface{}) {
	fmt.Fprintf(io.writer, format, a...)
}

func (io *Io) PrintIntSlice(a []int) {
	b := make([]interface{}, 0, len(a))
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func (io *Io) PrintStringSlice(a []string) {
	b := make([]interface{}, 0, len(a))
	for _, x := range a {
		b = append(b, x)
	}
	io.Println(b...)
}

func Log(name string, value interface{}) {
	fmt.Fprintf(os.Stderr, "%s=%+v\n", name, value)
}

func ExampleIo() {
	io := NewIo()
	defer io.Flush()
	a := make([]int, 0, 3)
	a[0], a[1], a[2] = io.NextInt(), io.NextInt(), io.NextInt()
	io.Println(a)
	io.PrintIntSlice(a)
	Log("io", a)
}

C++: #define _USE_MATH_DEFINES
#include<iostream>
#include<string>
#include<cmath>
#include<queue>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<random>
#include<functional>
#include<algorithm>
#include<cstdio>
#include<unordered_map>
using namespace std;
//---------------------------------------------------
//ライブラリゾーン！！！！
typedef long long ll;
typedef long double ld;
#define str string
#define rep(i,j) for(ll i=0;i<(long long)(j);i++)
const ll Mod = 1000000007;
const ll gosenchou = 5000000000000000;
short gh[2][4] = { { 0,0,-1,1 },{ -1,1,0,0 } };
struct P {
	ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B {//隣接リスト表現
	ll to;
	ld cost;
};
struct E {//辺の情報を入れる変数
	ll from, to, cost;
};
bool operator<(E a, E b) {
	return a.cost < b.cost;
}
struct H {
	ll x, y;
};
bool operator<(H a, H b) {
	if (a.x != b.x) return a.x < b.x;
	return a.y < b.y;
}
bool operator>(H a, H b) {
	if (a.x != b.x) return a.x > b.x;
	return a.y > b.y;
}
bool operator==(H a, H b) {
	return a.x == b.x&&a.y == b.y;
}
bool operator!=(H a, H b) {
	return a.x != b.x || a.y != b.y;
}
ll gcm(ll i, ll j) {//最大公約数
	if (i > j) swap(i, j);
	if (i == 0) return j;
	return gcm(j%i, i);
}
ld rad(H a, H b) {
	return sqrt(pow(a.x - b.x, 2.0) + pow(a.y - b.y, 2.0));
}//rad＝座標上の2点間の距離
ll ari(ll a, ll b, ll c) {
	return (a + b)*c / 2;
}//等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
	if (b <= c || d <= a) return 0;
	return 1;
}//[a,b),[c,d)
ll fact(ll x, ll k,ll p) {//最大値、個数
	ll sum = 1;
	for (int i = 0; i < k; i++) {
		sum *= (x--);
		sum %= p;
	}
	return sum;
}//階乗(正）
ll mod_pow(ll x, ll n, ll p) {
	ll res = 1;
	while (n > 0) {
		if (n & 1) res = res*x%p;
		x = x*x%p;
		n >>= 1;
	}
	return res;
}//x^n%p
#define int long long
const long long inf = 4523372036854775807;
const int iinf = 1500000000;
//----------------------------------------------------
//++++++++++++++++++++++++++++++++++++++++++++++++++++
int n, k, s;
int solve(int x, int y, int z) {
	if (x == k) {
		if (z == s) return 1;
		else return 0;
	}
	int sum = 0;
	for (int i = y + 1; i + (k - x) - 1 <= n&&z + ari(i, i + (k - x) - 1, (k - x)) <= s; i++) {
		sum += solve(x + 1, i, z + i);
	}
	return sum;
}
signed main() {
	while (cin >> n >> k >> s&&n + k + s > 0) {
		cout << solve(0, 0, 0) << endl;
	}
	getchar(); getchar();
}

C++: #include <stdio.h>
#include <cctype>
#include <limits.h>
#include <math.h>
#include <complex>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cstring>
#include <string>
#include <sstream>
#include <algorithm>
#include <iomanip>
#include <iostream>

#define VARIABLE(x) cerr << #x << "=" << x << endl
#define BINARY(x) static_cast<bitset<16> >(x)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define REP(i,m,n) for (int i=m;i<(int)(n);i++)
#define if_range(x, y, w, h) if (0<=(int)(x) && (int)(x)<(int)(w) && 0<=(int)(y) && (int)(y)<(int)(h))

const int INF = 1e9;
const double EPS = 1e-8;
const double PI = 3.14159;
int dx[4]={0, 1, 0, -1}, dy[4]={-1, 0, 1, 0};
using namespace std;
typedef long long ll;
typedef pair<int, int> P;

/* struct P {
	int x, y, n;
	P(int n, int x, int y):n(n), x(x), y(y){}
	P(){}
}; */


/** Problem1335 : Equal Sum Sets **/
int N, K, S;
int dp[21][11][151];
int solve(int n, int k, int s)
{
	//cerr << n << " " << k << " " << s << endl;
	if (k == K)
		return S==s;
	if (n>N)
		return 0;
	if (dp[n][k][s]>=0) return dp[n][k][s];
	
	int res=0;
	res += solve(n+1, k, s);
	res += solve(n+1, k+1, s+n);
	return dp[n][k][s] = res;
}

int main()
{
	while (cin>>N>>K>>S, N) {
		memset(dp, -1, sizeof(dp));
		cout << solve(1, 0, 0) << endl;
	}
}

C++: #include<bits/stdc++.h>
using namespace std;

#define REP(i,n) for(int i=0;i<(n);i++)
#define ALL(v) (v).begin(),(v).end()
#define int long long
typedef pair<int,int> P;

//-----------------------------------------------------------------------

signed main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n,k,s;
    while(cin>>n>>k>>s,n)
    {
        int ans=0;
        REP(b,1<<n){
            if(__builtin_popcount(b)!=k) continue;
            int sum=0;
            REP(i,n){ 
                if(b>>i&1) sum+=i+1;
            }
            if(sum==s) ans++;
        }
        cout<<ans<<endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
#include<queue>
#include<list>
using namespace std;
int inf = 1000000000;


int main(void) {

  int n, k, s;
  while(cin >> n >> k >> s){
    if( n == 0 ) break;

    int dp[21][21][156] = {};
    dp[0][0][0] = 1;
    for(int i=1; i<=n; i++){
      for(int j=0; j<=k; j++){
        for(int l=0; l<=s; l++){
          if( l >= i && j != 0 ) dp[i][j][l] += dp[i-1][j-1][l-i];
          dp[i][j][l] += dp[i-1][j][l];
        }
      }
    }
    cout << dp[n][k][s] << endl;

  }


  return 0;
}

// EOF

C++: #include<iostream>
using namespace std;

int n, k, s;
int ans;

void dfs(int i, int k, int s){
    if(k == 0){
        if(s == 0)  ans++;
        return;
    }

    if(i > n || i > s)   return;

    dfs(i+1, k-1, s-i);
    dfs(i+1, k, s);
}

int main(){
    while(cin >> n >> k >> s, n+k+s){
        ans = 0;
        dfs(1, k, s);
        cout << ans << endl;
    }
    return 0;
}