main(n,m,i,ans){
    ans=0;
    char s[10000];
    int u[2];
    int b[2];
    memset(u,0,8);
    memset(b,0,8);
    scanf("%d%d",&n,&m);
    scanf("%s",&s);
    for (;n--;)s[n]=='A'?u[0]++:u[1]++;
    scanf("%s",&s);
    for (;m--;)s[m]=='A'?b[0]++:b[1]++;
    for (i=2;i--;)u[i]>=b[i]?ans+=b[i]:(ans+=u[i]);
    printf("%d",ans);
}