#include<bits/stdc++.h>
using namespace std;
int f(int k)
{
if (k <= 1) return 1;
else return k*f(k-1);
}
main()
{
int n,r;
scanf("%d%d", &n, &r);
printf("%d", f(n) / f(r) / f(n-r) );
return 0;
}
#include<cstdio>
#include<cmath>
int main(){
int n;
scanf("%d", &n);
long long int ans = pow(2, n) - 1;
printf("%lld\n", ans);
}
#include<cstdio>
int main(){
float m,b,a;
scanf("%f", &m);
scanf("%f", &b);
a= -b/m;
printf("%.4f\n",a);
}
#include<cstdio>
int n, ans;
int f(int num){
int a = 0, b = num;
while(b){
if(b%10 == 3 || b%10 == 6 || b%10 == 9) a++;
b/=10;
}
return a;}
int main(){
scanf("%d", &n);
for(int i = 1; i <= n; i++) ans += f(i);
printf("%d", ans);}
#include<cstdio>(5각수 small)
int main(){
int i,j,k,s;
scanf("%d",&i);
i+=1;
k = ((i*3 -1) * i) / 2;
printf("%d",k);
}
#include<cstdio>(5각수 large)
int main(){
unsigned long long int i,j,k,s;
scanf("%lu",&i);
i+=1;
k = ((i*3 -1) * i) / 2;
printf("%lu",k%1000000004);
}