一本通1029

//qf
#include <bits/stdc++.h>
#define f(i,j,n) for(register int i=j;i<=n;i++)
using namespace std;
typedef long long ll;
inline ll read() {
	ll x=0;
	int f=1;
	char ch=getchar();
	while(!isdigit(ch)) {
		if(ch=='-') f=-1;
		ch=getchar();
	}
	while(isdigit(ch)) x=(x<<1)+(x<<3)+(ch-48),ch=getchar();
	return x*f;
}
double d,D,r; 
signed main() {
	cin>>d>>D;
	r=d-int(d/D)*D;
	cout<<r<<endl;
	return 0;
}