#include <iostream>
#include <fstream>

int n, k, *vect;

unsigned long getResult(int n, int k, int i, int *vect){

    if (k > 0 && i == n)
        return 0;
    else if(!k)
        return 1;

    int *newVect = new int[n];
    for(int i=0; i<n; i++)
        newVect[i] = vect[i] - 1;

    return vect[i]*getResult(n, k-1, i+1, newVect) + getResult(n, k, i+1, vect);
}
int main(){

    std::ifstream read("turnuri.in");
    std::ofstream write("turnuri.out");

    read>>n>>k;
    vect = new int[n];

    for(int i=0; i<n; i++)
        read>>vect[i];

    unsigned long result = getResult(n, k, 0, vect);
    std::cout<<result<<std::endl;
    return 0;
}