Ural 1114 Boxes

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 21;
 4 unsigned long long dp[maxn][maxn][maxn];
 5 int main() {
 6     int N,A,B;
 7     while(~scanf("%d%d%d",&N,&A,&B)) {
 8         memset(dp,0,sizeof dp);
 9         dp[0][0][0] = 1;
10         for(int i = 1; i <= N; ++i)
11             for(int j = 0; j <= A; ++j)
12                 for(int k = 0; k <= B; ++k)
13                     for(int a = 0; a <= j; ++a)
14                         for(int b = 0; b <= k; ++b)
15                             dp[i][j][k] += dp[i-1][a][b];
16         unsigned long long ret = 0;
17         for(int i = 0; i <= A; ++i)
18             for(int j = 0; j <= B; ++j)
19                 ret += dp[N][i][j];
20         printf("%I64u\n",ret);
21     }
22     return 0;
23 }