#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

const int inf=1e9+;

int read(){

    int ans=,f=,c=getchar();

    while(c<''||c>''){if(c=='-') f=-; c=getchar();}

    while(c>=''&&c<=''){ans=ans*+(c-''); c=getchar();}

    return ans*f;

}

int n,m,head=,top,ans;

int s[],a[],sum[],mn[];

int main(){

    n=read(); m=read(); top=n;

    sum[]=inf; mn[]=;

    for(int i=;i<=n;i++){

        s[i]=read();

        sum[i]=sum[i-]; mn[i]=mn[i-];

        if(s[i]<=sum[i]) sum[i]=s[i],mn[i]=i;

    }

    for(int i=;i<=m;i++) a[i]=read();

    while(top&&head<=m){

        if(sum[top]>=a[head]) ans++,head++,top--;

        else top=mn[top]-;

    }

    printf("%d\n",ans);

    return ;

}