#include <iostream>
#include <cstring> 
#include <cstdio>
using namespace std;
const int N=1e7+10;
int k,n,a[N],ans;
char s[N];
int main(){
	freopen("changgao_modulo.in","r",stdin);
	freopen("changgao_modulo.out","w",stdout); 
	scanf("%d",&k);
	scanf("%s",s+1);
	n=strlen(s+1);
	for(int i=1;i<=n;i++)a[i]=s[i]-'0';
	for(int i=n;i>=1;i--){
		a[i]=a[i]-a[i-1];
		a[i]=(a[i]%k+k)%k;
	}
	int cnt=0;
	for(int i=1;i<=n;i++){
		if(cnt>=a[i]){
			cnt-=a[i];
		}else{
			cnt+=k-a[i];
			ans+=k-a[i];
		}
	}
	printf("%d\n",ans);
	return 0;
}