题目链接
题解
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector>
#include<map>
#include<set>
using namespace std;
#define int long long
const int mod = 20100403,N = 2000010;
int Mod(int x){return (x%mod+mod)%mod;}
int qmi(int a,int b){int res=1;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res%mod;}
int fac[N],inv[N];
void init()
{
fac[0]=inv[0]=1;
for(int i=1;i<N;i++){
fac[i]=fac[i-1]*i%mod;
inv[i]=inv[i-1]*qmi(i,mod-2)%mod;
}
}
int C(int a,int b)
{
if(a==b||b==0)return 1;
if(b<0||b>a)return 0;
return fac[a]%mod*inv[b]%mod*inv[a-b]%mod;
}
signed main()
{
init();
int n,m;cin>>n>>m;
cout<<Mod(C(n+m,n)-C(n+m,m-1));
}