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

const int N = 2e6+10;

int n,k,ans;
char a[N],b[N];

int main(){
	freopen("cowreography.in","r",stdin);
	freopen("cowreography.out","w",stdout);
	scanf("%d%d",&n,&k);
	cin>>(a+1);
	cin>>(b+1);
	if(k==1){
		ans=0;
		int j=1,pre=1;
		for(int i=1;i<=n;i++){
			if(a[i]=='1'){
				while(b[j]!='1')j++;
				pre=j;
				ans+=abs(i-j); 
				j++;
//				cout<<i<<" "<<j<<endl;
			}
		}
		printf("%d",ans);
	} 
	return 0;
}