#include <cstdio>
#include <algorithm>

using namespace std;

#define file_in "bile2.in"
#define file_out "bile2.out"

#define Baza 10000
#define Nmax 1020

char s[Nmax];
int comb[2][Nmax][Nmax/10];
int c[2][Nmax][Nmax/10];
int a[Nmax];
int b[Nmax];
int s1[Nmax];
int s2[Nmax];
int s3[Nmax];
//long long comb[1001][1001],a,b,c[1001][1001];
int n,d;

void add(int A[], int B[])
{
      int i, t = 0;
      for (i=1; i<=A[0] || i<=B[0] || t; i++, t/=Baza)
              A[i] = (t += A[i] + B[i]) % Baza;
      A[0]=i-1;
}

void mul(int A[], int B)
{
      int i, t = 0;
      for (i = 1; i <= A[0] || t; i++, t /= Baza)
              A[i] = (t += A[i] * B) % Baza;
      A[0] = i - 1;
}

void Mul(int A[], int B[])
{
      int i, j, t, C[Nmax];
      memset(C, 0, sizeof(C));
      for (i = 1; i <= A[0]; i++)
      {
              for (t=0, j=1; j <= B[0] || t; j++, t/=Baza)
                      C[i+j-1]=(t+=C[i+j-1]+A[i]*B[j])%Baza;
              if (i + j - 2 > C[0]) C[0] = i + j - 2;
      }
      memcpy(A, C, sizeof(C));
}

void sub(int A[], int B[])
{
      int i, t = 0;
      for (i = 1; i <= A[0]; i++)
              A[i] += (t = (A[i] -= B[i] + t) < 0) * Baza;
      for (; A[0] > 1 && !A[A[0]]; A[0]--);
}

void div(int A[], int B)
{
      int i, t = 0;
      for (i = A[0]; i > 0; i--, t %= B)
              A[i] = (t = t * Baza+ A[i]) / B;
      for (; A[0] > 1 && !A[A[0]]; A[0]--);
}



void init(int A[], int B)
{
	do
	{
		A[++A[0]]=B%Baza;
		B/=Baza;
	}
	while(B);
}

void print(int A[])
{
   int i;
   printf("%d",A[A[0]]);
   for (i=A[0]-1;i>=1;--i)
	    printf("%.04d",A[i]);
}


int cmp(int A[], int B[])
{
	int i;

	if (A[0]>B[0]) 
		return 1;
	if (A[0]<B[0]) 
		return -1;
	for (i=A[0];i>=1;--i)
		if (A[i]>B[i]) 
			return 1;
		else 
		if (A[i]<B[i]) 
			return -1;
	return 0;
}
 	   

int main()
{
	int i,j,t,ind,stp,l;
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	scanf("%d %d\n", &n, &d);
		
	scanf("%s\n", s);
	l=strlen(s);
	for (i=1;i<=l;i+=4)
	{
		++a[0];
		for (j=3;j>=0;--j)
			if (l-i-j>=0)
				a[a[0]]=a[a[0]]*10+s[l-i-j]-'0';
	}
 
	scanf("%s\n", s);
	l=strlen(s);
	for (i=1;i<=l;i+=4)
	{
		++b[0];
		for (j=3;j>=0;--j)
			if (l-i-j>=0)
				b[b[0]]=b[b[0]]*10+s[l-i-j]-'0';
	}

	memcpy(s3,b,sizeof(s3));
  /* print(a);
   printf("\n");
   print(b);
   printf("\n");*/
	
	
	//merg cu comb
	init(comb[0][0],1);
	
	ind=1;
	for (i=1;i<=n;++i,ind^=1)
	{
		memset(comb[ind],0,sizeof(comb[ind]));
	    init(comb[ind][0],1);
		for (j=1;j<=n;++j)
		{
			add(comb[ind][j],comb[ind^1][j-1]);
			add(comb[ind][j],comb[ind^1][j]);
		}
	}		
	
	stp=ind^1;
    ind=1;
	//merg cu c
	for (i=0;i<=n;++i)
	init(c[0][i],1);
	
    for (i=1;i<=n;++i,ind^=1)
	{
		memset(c[ind],0,sizeof(c[ind]));
		//init(c[ind][i],1);
		for (j=1;j<=n;++j)
		{
			add(c[ind][j],c[ind][j-1]);
			add(c[ind][j],c[ind^1][max(j-d-1,0)]);
		}
		
		//if (comb[n][i]*(b-a)>=b*c[i][n])

		memcpy(s1,comb[stp][i],sizeof(s1));
		memcpy(b,s3,sizeof(b));
		sub(b,a);
		Mul(s1,b);
		memcpy(s2,c[ind][n],sizeof(s2));
		Mul(s2,s3);
		
		if (cmp(s1,s2)>=0)
		{
			printf("%d\n", i);
			break;
		}
	}

			
	fclose(stdin);
	fclose(stdout);
	
	return 0;
	
}