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

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)

#define ll long long
#define ull unsigned ll

void reader(int *x){int k,m=0;*x=0;for(;;){mygc(k);if(k=='-'){m=1;break;}if('0'<=k&&k<='9'){*x=k-'0';break;}}for(;;){mygc(k);if(k<'0'||k>'9')break;*x=(*x)*10+k-'0';}if(m)(*x)=-(*x);}
void reader(ll *x){int k,m=0;*x=0;for(;;){mygc(k);if(k=='-'){m=1;break;}if('0'<=k&&k<='9'){*x=k-'0';break;}}for(;;){mygc(k);if(k<'0'||k>'9')break;*x=(*x)*10+k-'0';}if(m)(*x)=-(*x);}
void reader(double *x){scanf("%lf",x);}
int reader(char c[]){int i,s=0;for(;;){mygc(i);if(i!=' '&&i!='\n'&&i!='\r'&&i!='\t'&&i!=EOF) break;}c[s++]=i;for(;;){mygc(i);if(i==' '||i=='\n'||i=='\r'||i=='\t'||i==EOF) break;c[s++]=i;}c[s]='\0';return s;}
template <class T, class S> void reader(T *x, S *y){reader(x);reader(y);}
template <class T, class S, class U> void reader(T *x, S *y, U *z){reader(x);reader(y);reader(z);}
template <class T, class S, class U, class V> void reader(T *x, S *y, U *z, V *w){reader(x);reader(y);reader(z);reader(w);}

void writer(int x, char c){int s=0,m=0;char f[10];if(x<0)m=1,x=-x;while(x)f[s++]=x%10,x/=10;if(!s)f[s++]=0;if(m)mypc('-');while(s--)mypc(f[s]+'0');mypc(c);}
void writer(ll x, char c){int s=0,m=0;char f[20];if(x<0)m=1,x=-x;while(x)f[s++]=x%10,x/=10;if(!s)f[s++]=0;if(m)mypc('-');while(s--)mypc(f[s]+'0');mypc(c);}
void writer(double x, char c){printf("%.15f",x);mypc(c);}
void writer(const char c[]){int i;for(i=0;c[i]!='\0';i++)mypc(c[i]);}
void writer(const char x[], char c){int i;for(i=0;x[i]!='\0';i++)mypc(x[i]);mypc(c);}
template<class T> void writerLn(T x){writer(x,'\n');}
template<class T, class S> void writerLn(T x, S y){writer(x,' ');writer(y,'\n');}
template<class T, class S, class U> void writerLn(T x, S y, U z){writer(x,' ');writer(y,' ');writer(z,'\n');}
template<class T> void writerArr(T x[], int n){int i;if(!n){mypc('\n');return;}rep(i,n-1)writer(x[i],' ');writer(x[n-1],'\n');}

char memarr[17000000]; void *mem = memarr;
#define MD 1000000007

template<class T>
int editDistance(int As, T A[], int Bs, T B[], void *mem){
  int i, j, k;
  int *dp = (int*)mem;

  rep(i,As+1) dp[i*(Bs+1)] = i;
  rep(i,Bs+1) dp[i] = i;
  
  REP(i,1,As+1) REP(j,1,Bs+1){
    k = min(dp[i*(Bs+1)+j-1], dp[(i-1)*(Bs+1)+j]) + 1;
    if(A[i-1]==B[j-1]) k = min(k, dp[(i-1)*(Bs+1)+(j-1)]);
    else               k = min(k, dp[(i-1)*(Bs+1)+(j-1)]+1);
    dp[i*(Bs+1)+j] = k;
  }

  return dp[As*(Bs+1)+Bs];
}



#define SSE2_M128I_ADD32(c,a,b) asm volatile("movdqu %1, %%xmm0;" "movdqu %2, %%xmm1;" "paddd %%xmm1, %%xmm0;" "movdqu %%xmm0, %0;" :"=m"(c) :"m"(a), "m"(b) :);
#define SSE4_M128I_MIN32(c,a,b) asm volatile("movdqu %1, %%xmm0;" "movdqu %2, %%xmm1;" "pminsd %%xmm1, %%xmm0;" "movdqu %%xmm0, %0;" :"=m"(c) :"m"(a), "m"(b) :);
#define SSE2_M128I_EQ32(c,a,b) asm volatile("movdqu %1, %%xmm0;" "movdqu %2, %%xmm1;" "pcmpeqd %%xmm1, %%xmm0;" "movdqu %%xmm0, %0;" :"=m"(c) :"m"(a), "m"(b) :);
#define SSE2_M128I_NEQ32(c,a,b) asm volatile("movdqu %1, %%xmm0;" "movdqu %2, %%xmm1;" "pcmpeqd %%xmm1, %%xmm0;" "pcmpeqd %%xmm1, %%xmm1;" "pxor %%xmm1, %%xmm0;" "movdqu %%xmm0, %0;" :"=m"(c) :"m"(a), "m"(b) :);
#define SSE2_M128I_AND(c,a,b) asm volatile("movdqu %1, %%xmm0;" "movdqu %2, %%xmm1;" "pand %%xmm1, %%xmm0;" "movdqu %%xmm0, %0;" :"=m"(c) :"m"(a), "m"(b) :);
#define SSE4_M128U_CHAR2INT(c,a) asm volatile("movdqu %1, %%xmm0;" "pmovzxbd %%xmm0, %%xmm1;" "movdqu %%xmm1, %0;" :"=m"(c) :"m"(a) :);

int SSE4_editDistance(int As, char A[], int Bs, char B[], void *mem){
  int i, j, k;
  int *dp = (int*)mem;
  unsigned one[4] = {1,1,1,1}, t1[4], t2[4], aa[4], bb[4];

  rep(i,As+1) dp[i*(Bs+1)] = i;
  rep(i,Bs+1) dp[i] = i;
  
  REP(i,1,As+1){
    rep(j,4) aa[j] = A[i-1];
    for(j=1;j+3<Bs+1;j+=4){
      SSE4_M128U_CHAR2INT(bb, B[j-1]);
      
      SSE4_M128I_MIN32(t1, dp[i*(Bs+1)+j-1], dp[(i-1)*(Bs+1)+j]);
      SSE2_M128I_ADD32(t1, t1, one);

      SSE2_M128I_NEQ32(t2, aa, bb);
      SSE2_M128I_AND(t2, t2, one);
      SSE2_M128I_ADD32(t2, t2, dp[(i-1)*(Bs+1)+(j-1)]);

      SSE4_M128I_MIN32(dp[i*(Bs+1)+j], t1, t2);
    }
    REP(j,j,Bs+1){
      k = min(dp[i*(Bs+1)+j-1], dp[(i-1)*(Bs+1)+j]) + 1;
      if(A[i-1]==B[j-1]) k = min(k, dp[(i-1)*(Bs+1)+(j-1)]);
      else               k = min(k, dp[(i-1)*(Bs+1)+(j-1)]+1);
      dp[i*(Bs+1)+j] = k;
    }
  }

  return dp[As*(Bs+1)+Bs];
}


int As, Bs;
char A[1200], B[1200];

int main(){
  int res;

  reader(&As,&Bs);
  reader(A,B);

  res = editDistance(As, A, Bs, B, mem);
  writerLn(res);
//  res = SSE4_editDistance(As, A, Bs, B, mem);
//  writerLn(res);
  
  return 0;
}