#include <iostream>
using namespace std;

//计算n的阶乘 
int jc(int n){
    int i,res=1;
    for(i=1;i<=n;i++){
        res=res*i;
    } 
    return res;
}

//计算组合数
int C(int m,int n){
    return (jc(n))/(jc(m)*jc(n-m));
} 

int main(void)
{
    int n,a,b;
    cin>>n>>a>>b;
    
    cout<<2+C(n-2,b-a+1)<<endl;
    return 0;
}