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++: #include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <bitset>
#include <numeric>

using namespace std;
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }
typedef pair<int, int> P;
typedef long long ll;
typedef unsigned long long ull;

#define For(i,a,b)	for(int (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define rall(a)		(a).rbegin(), (a).rend()
#define sz(a)		(sizeof(a))
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)
#define fi first
#define se second
bool cheak(int x, int y, int xMax, int yMax){ return x >= 0 && y >= 0 && xMax > x && yMax > y; }
const int dx[4] = { -1, 0, 1, 0 }, dy[4] = { 0, 1, 0, -1 };
const int mod = 1000000007;
const int INF = 1e9;

int main()
{
	int n, k, s;

	while (cin >> n >> k >> s && n){

		int ans = 0;
		rep(i, (1 << n) + 1)if (__builtin_popcount(i) == k){
			
			int v = 0;
			rep(j, n){
				if ((i >> j ) & 1){
					v += j+1;
				}
			}

			if (v == s){
				ans++;
			}
		}
		cout << ans << endl;
	}
	return 0;
}

C++: #include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };
int cnt;
int n, k, s;
void dfs(int add,int sum,int re) {
	if (k == re) {
		if (sum == s)
			cnt++;
		return;
	}
	for (int i = add + 1;i < s - add*(k - re)&&i<=n;i++) {
		dfs(i, sum + i, re + 1);
	}
}
int main() {
	
	while (cin >> n >> k >> s, n){
		cnt = 0;
		dfs(0,0,0);
		cout << cnt << endl;
	}
}

C++: #include <numeric>
#include <vector>
#include <algorithm>
using namespace std;

int main(){
    int n,k,s,i,c,res;
    while(1){
        scanf("%d",&n);
        scanf("%d",&k);
        scanf("%d",&s);
        if(!n && !k && !s){break;}
        vector<int> t(n,0);
        vector<int> cd(n);
        iota(cd.begin(),cd.end(),1);
        for(i=0;i<k;i++){t[n-i-1]=1;}    
        res=0;
        do{
            c=0;
            for(i=0;i<n;i++){c+=(t[i]*cd[i]);}
            if(c==s){res++;}
        } while(next_permutation(t.begin(),t.end()));
        printf("%d\n",res);
    }
    return 0;
}

C++: #include <iostream>

using std::cin;
using std::cout;
using std::endl;

int dfs(int n, int sum, int k, int sn) {
	int ret = 0;
	if (k == 0) {
		if (sn == sum) {
			return 1;
		}
		else {
			return 0;
		}
	}
	if (sn > sum || n == 0) {
		return 0;
	}

	ret += dfs(n-1, sum, k-1, sn+n);
	ret += dfs(n-1, sum, k, sn);
	
	return ret;
}

int main(void) {
	int n,k,s;
	cin >> n;
	cin >> k;
	cin >> s;

	while ( n != 0 || k != 0 || s!= 0 ) {
		int count = dfs(n,s,k,0);
		cout << count << endl;

		cin >> n;
		cin >> k;
		cin >> s;
	}

	return 0;
}

C++: #include <iostream>

using namespace std;

int cnt = 0;

void search(int n, int k, int s) {
    if (k==0&&s==0) {
        cnt++;
        return;
    }
    if (k<=0||s<=0)
        return;
    for (int i = n; i > 0; i--)
        search(i-1, k-1, s-i);
}

int main() {
    int n, k, s;
    while (cin >> n >> k >> s, n|k|s) {
        cnt = 0;
        search(n, k, s);
        cout << cnt << endl;
    }
}

C++: #include<iostream>
#include<vector>
using namespace std;
// next_combination version
// given an integer cur, next_combination returns an integer nxt s.t.
//   nxt has the same number of 1s as cur
//   nxt is bigger than cur
//   no integer between cur and nxt has the same number of 1s as cur (and nxt)
int next_combination(int cur)
{
  int r1 = cur & -cur;   // extracts the rightmost 1
  int moved1 = cur + r1; // cancel the rightmost run of 1s and put 1 on its left
  int rm1s = cur & ~moved1; // extracts the rightmost run of 1s
  int reset = (rm1s / r1) >> 1; // the run of 1s moved to LSD and made its length decreased by 1
  int nxt = moved1 | reset; // new combination
  return nxt;
}
int main(int argc, char *argv[])
{
  for(;;) {
    int n, k, s;
    cin >> n >> k >> s;
    if(n == 0 && k == 0 && s == 0) break;
    int cnt = 0;
    if(k <= n) {
      const int fin = ((1<<k) - 1) << (n-k);
      for(int i = (1<<k) - 1; i <= fin; i = next_combination(i)) {
		int ss = 0, ii = i;
		while(ii != 0) {
		  int x = ii & -ii;
		  ii ^= x;
		  ss += __builtin_ffs(x);
		}
        if(s == ss) cnt++;
      }
    }
    cout << cnt << endl;
  }
  return 0;
}