/*
      Creator :  bizarre
    */
    #include <bits/stdc++.h>
    #include <math.h>
    using namespace std;
    #define bizarre  ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    #define file freopen("input.txt","r",stdin); freopen("output.txt","w",stdout);
    #define ll long long
    #define ld long double
    #define pi acos(-1)
    #define point complex<double>
    const int N = 1e6 + 9, inf = 2e9, mod = 1e9 + 7;
    vector<int> prime_Numbers;
    bool primes[1000005];
    double dot(point a, point b)
    {
        return (conj(a) * b).real();
    }
    double cross(point a, point b)
    {
        return (conj(a) * b).imag();
    }
    /*
    void prime(int n)
    {
        primes[1]=primes[0]=0;
        for(int i=2; i<=n; i++)
            primes[i]=true;
        for(int i=2; i<=n; i++)
        {
            if(primes[i]==true)
            {
                prime_Numbers.push_back(i);
                for(int j=i+i; j<=n; j+=i)
                    primes[j]=false;
            }
        }
    }
    void move1step(long long& a, long long& b, long long q)
    {
        long long c= a-q*b;
        a=b;
        b=c;
    }
    long long egcd(long long r0,long long r1,long long& x0,long long& y0)
    {
        long long x1=0,y1=1;
        x0=1;
        y0=0;
        while(r1)
        {
            long long q=r0/r1;
            move1step(r0,r1,q);
            move1step(x0,x1,q);
            move1step(y0,y1,q);
        }
        return r0;
    }
    bool  solve (long long a, long long b, long long c,long long&x, long long& y)
    {
        long long g=egcd(a,b,x,y);
        int m=c/g;
        x*=m;
        y*=m;
        return c%g==0;
    }
    int gcd(int a, int b)
    {
        if(b==0)
            return a;
        return gcd(b,a%b);
    }
    void PrimeFactorization(int n)
    {
        for(int i=2; i*i<=n; i++)
        {
            int c=0;
            if(n%i==0)
            {
                while(n%i==0)
                {
                    n/=i;
                }

            }
        }

    }
    long long ncrtane(long long n, long long r)
    {
        long long ans=1,cntr=1;
        for(int i=n; i>n-r; i--)
        {
            ans*=i;
            ans/=cntr;
            cntr++;
        }
        return ans;
    }
    int ncr(long long n, long long r)
    {
        return (((fact[n] * inv[n - r]) % mod) * inv[r]) % mod;
    }

    int npr(long long n, long long r)
    {
        return (fact[n] * inv[n - r]) % mod;
    }
    long long fact[N], inv[N];
    long long fp(long long base, long long exp)
    {
        if (exp == 0)
            return 1;
        long long ans = fp(base, exp / 2);
        ans = (ans * ans) % mod;
        if (exp % 2 != 0)
            ans = (ans * (base % mod)) % mod;
        return ans;
    }

    void pre(long long n)
    {
        fact[0] = 1;
        inv[0] = 1;
        for (long long i = 1; i <= n; i++)
        {
            fact[i] = (i * fact[i - 1]) % mod;
            inv[i] = fp(fact[i], mod - 2);
        }
    }
    */
    /*
    ll lfts,lftw;
    ll p,f,cnts,cntw,s,w;
    ll ss(ll cnts, ll cntw, ll mxmp)
    {
         for(int i = 0;i<=cnts;i++)
            {
                ll var = i*s,s = 0,e = cntw,mid,ans;
                if(var>p)break;
                while(s<=e)
                {
                    mid = (s+e)/2;
                    if((mid*w)+var<=p)ans = mid,s = mid+1;
                    else e = mid-1;
                }
                if(mxmp<i+mid)mxmp = i+mid,lfts-=i,lftw-=mid;
            }
            return mxmp;
    }
    ll ww(ll cnts, ll cntw, ll mxmp)
    {
        for(int i = 0;i<=cnts;i++)
            {
                ll var = i*s,s = 0,e = cntw,mid,ans;
                if(var>f)break;
                while(s<=e)
                {
                    mid = (s+e)/2;
                    if((mid*w)+var<=f)ans = mid,s = mid+1;
                    else e = mid-1;
                }
                if(mxmp<i+mid)mxmp = i+mid;
            }
            return mxmp;
    }
    */
    int main()
    {
        bizarre
        ll n,k;
        cin >> n >> k;
        ll a[n+2];
        for(int i = 0;i<n;i++)cin >> a[i];
        ll ans = 0;
        ll sum = 0;
        while(sum<n)
        {
            ans++;
            if(!sum)sum++;
            sum+=k;
            sum--;
        }
        cout << ans;
        return 0;
    }


Measured memory_bytes: 4340