//#include "stdafx.h"

#include<cstdio>

#include<cctype>

#include<vector>

#include<algorithm>

using namespace std;

int n=7;

?char s[211000]="trivial";

?char t[211000]="problem";

int main(){??

? scanf("%d",&n);?

scanf("%s",s);scanf("%s",t);

/*

int i;

for (i=0;i<n;i++)

{

char ch;

ch=getchar();

if(ch!=10 && ch!=13)s[i]=ch;

else i--;

}

for ( i=0;i<n;i++)

{

char ch;

ch=getchar();

if(ch!=10 && ch!=13)t[i]=ch;

else i--;

}*/

?

long? ?long sum=0;?

int si=n-1;

int flag=0;

? ?

while( si? !=-1)??

{

if(? ?*(s+si )<= *(t+ si ))

{

if(*(s+si)< *(t+si)){

flag=si;

sum+=n-si;

//printf("in %d,? %s,? k=%d\n",n-si, s+si,si);

}

else if( flag? )sum+=n-flag;

}

else flag=0;

?

si--; ?

}

printf("%lld\n",sum);?

return 0;

}