来啦

#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>
using namespace std;

// 大数加法
vector<int> add(vector<int> a, vector<int> b) {
    vector<int> res;
    int carry = 0;
    int i = 0;
    while (i < a.size() || i < b.size() || carry) {
        int sum = carry;
        if (i < a.size()) sum += a[i];
        if (i < b.size()) sum += b[i];
        res.push_back(sum % 10);
        carry = sum / 10;
        i++;
    }
    return res;
}

// 大数乘以整数
vector<int> mul(vector<int> a, int b) {
    vector<int> res;
    int carry = 0;
    for (int i = 0; i < a.size() || carry; i++) {
        int sum = carry;
        if (i < a.size()) sum += a[i] * b;
        res.push_back(sum % 10);
        carry = sum / 10;
    }
    return res;
}

// 打印大数
void print(vector<int> v) {
    for (int i = v.size() - 1; i >= 0; i--) {
        cout << v[i];
    }
    cout << endl;
}

vector<int> stirling[105][105];

int main() {
    // 预处理到 100
    for (int i = 0; i <= 100; i++) {
        for (int j = 0; j <= 100; j++) {
            stirling[i][j].push_back(0);
        }
    }
    
    stirling[0][0] = {1};
    
    for (int n = 1; n <= 100; n++) {
        for (int m = 1; m <= n; m++) {
            // S(n,m) = m * S(n-1,m) + S(n-1,m-1)
            stirling[n][m] = add(mul(stirling[n-1][m], m), stirling[n-1][m-1]);
        }
    }
    
    int N, M;
    while (cin >> N >> M) {
        if (M > N || M == 0) {
            cout << 0 << endl;
        } else {
            vector<int> res = stirling[N][M];
            while (res.size() > 1 && res.back() == 0) res.pop_back();
            print(res);
        }
    }
    return 0;
}