/*
TASK: seq
LANG: C++
*/
# include <stdio.h>
# include <stdlib.h>
# define MAXN (1<<20)

long long n,k,br,ans;
long long num[MAXN],data[MAXN],temp[MAXN];


void read() {
    scanf("%lld %lld", &n,&k);
    for(int i = 1; i <= n; i++) {
        scanf("%lld", &num[i]);            
    }      
}

void solve() {
    if(k == 0) {
         for(int i = 1; i <= n; i++) {
             ans+=num[i];            
         }
         printf("%lld\n", ans);
         exit(0);     
    }
    
    for(int i = 1; i <= n; i++) {
        data[i] = n-i;            
    }
    
    for(int i = 3; i <= k; i++) {
        
        for(int j = n-i+1; j > 0; j--) {
            temp[j] = data[j+1]+temp[j+1];        
        }
        for(int i = 1; i <= n; i++) {
                 data[i] = temp[i];
                 temp[i] = 0;
        }            
    }
    //for(int i = 1; i <= n; i++) printf("%lld ", data[i]);        
    for(int i = 1; i <= n; i++) {
         br+=data[i];           
    }
    br = br*(n-k);
    br = br/n;
    for(int i = 1; i <= n; i++) {
        ans += num[i]*br;            
    }
    printf("%lld\n",ans);
}

int main() {
    read();
    solve();
    return 0;
}
