1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
#include <bits/stdc++.h>

using namespace std;

#define st first
#define nd second
#define pb push_back
#define sz(x) (int)(x).size()
#define ll long long
ll mod=1000000007;
int inf=1000000007;
ll infl=1000000000000000007;

ll DP[2][10000007];

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    ll n,m,ans=0;
    cin>>n>>m>>mod;
    for(ll i=1;i<=m;i++) DP[1][i]=m-i+1;
    for(ll i=2;i<=n;i++)
    {
        ll cnt=0,add=0,act=0;
        for(ll j=1;j<m;j++)
        {
            cnt=(cnt+DP[(i-1)%2][j])%mod;
            cnt=((cnt-DP[(i-1)%2][m-j+1])+mod)%mod;
        }
        for(ll j=m;j>0;j--)
        {
            add=(DP[(i-1)%2][j]*(m-j+1)+add)%mod;
            DP[i%2][j]=(add+cnt*(m-j+1))%mod;
            cnt=(cnt+DP[(i-1)%2][m-j+2])%mod;
            cnt=((cnt-DP[(i-1)%2][j-1])+mod)%mod;
        }
    }
    for(ll i=1;i<=m;i++) ans=(ans+DP[n%2][i])%mod;
    cout<<ans;
    return 0;
}