#include<bits/stdc++.h>
#define int __int128
using namespace std;

int c[101][101];
int ans;

//void dfs( int now, int lst ){
//	if( now == 0 ){
//		ans++;
//		return;
//	}
//	for( int i = lst; i <= now; i++ )
//		dfs( now-i,i );
//}

int read(){
	int num = 0;
	int x = 1;
	char ch = getchar();
	
	while( ch < '0' || '9' < ch ){
		if( ch == '-' )
			x = -1;
		ch = getchar();
	}
	
	while( '0' <= ch && ch <= '9' ){
		num = num*10+ch-'0';
		ch = getchar();
	}
	
	return num*x;
}

void write( int x ){
	if( x>10 )
		write(x/10);
	putchar(x%10+'0');
}

signed main(){
	 
	int n,a,b;
	
	n = read();
	a = read();
	b = read();

	
	int maxn = max(a,b);
		
	for( int i = 0; i <= n+maxn-1; i++ )
		c[i][0] = 1;
	
	for( int i = 1; i <= n+maxn-1; i++ )
		for( int j = 1; j <= i; j++ )
			c[i][j] = c[i-1][j] + c[i-1][j-1];
	
	int ans = 0;
	
	for( int i = 0; i <= a; i++ )
		for( int j = 0; j <= b; j++ )
			ans += c[n+i-1][n-1]*c[n+j-1][n-1];
	 
	write( ans );
	

	return 0;
}