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

bool isPrime(int n) {
    if (n <= 1)
        return false;
 
    for (int i = 2; i*i <= n ; i++)
        if (n % i == 0)
            return false;
 
    return true;
}
int nearPrime(int n) {
    if (n<=1){
        return 2;
    }
    int prime1 = n;
    int prime2 = n;
    bool found =false;
    while (!found) {
        prime1++;
 
        if (isPrime(prime1))
            found = true;
    }
    found =false;
    while (!found) {
        prime2--;
 
        if (isPrime(prime2))
            found = true;
    }
    if(prime1-n < n-prime2){
        return prime1;
    }
    else return prime2;
}
int32_t main()
{
    int n, k;
    int a[10000];
    int b[10000];
    int c[10000];
    int sum = 100000;

    cin >> n >>  k;
    for (int i=0;i<n;i++) {
        cin >> a[i];
    }
    for (int i=0;i<n;i++) {
        if (isPrime(a[i])) {
            b[i] = a[i];
        } else {
            b[i] = nearPrime(a[i]);
        }
        c[i] = abs(a[i] - b[i]);
    }
    
    /*for (int i=0;i<n;i++){
        cout<< c[i];
    }*/
    
    
    for (int i=0;i<n-k;i++) {
        int t = 0;
        for(int j = i; j< i+k;j++){
            t += c[j];
        }
        if(t < sum){
            sum = t;
        }
    }
    cout<< sum;
    return 0;
}