[51nod1043]幸运号码

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int mod=1e9+7;
ll dp[1002][9002];
int main(){
    int n;
    cin>>n;
    dp[0][0]=1; 
    for(int i=1;i<=n;i++){
        for(int j=0;j<=9*i;j++){
            for(int k=0;k<=9&&k<=j;k++){
                dp[i][j]+=dp[i-1][j-k];
                dp[i][j]%=mod;
            }
        }
    }
    ll ans=0;
    for(int i=0;i<=9*n;i++){
        ans+=dp[n][i]*(dp[n][i]-dp[n-1][i]);
        ans%=mod;
    }
    cout<<ans<<"\n";
    return 0;
}