delete pics to save space

7.3696.cpp

@@ -0,0 +1,44 @@
+#include<cstdio>
+typedef long long LL;
+LL L; int kase;
+LL gcd(LL a,LL b) { return b?gcd(b,a%b):a; }
+inline LL mmul(LL a, LL b, LL m)
+{
+	LL d=((long double)a/m*b+0.5);
+	LL r=a*b-d*m;
+	return r<0?r+m:r;
+}
+inline LL ksm(LL a,LL b,LL p)
+{
+	LL res=1;
+	for(;b;b>>=1,a=mmul(a,a,p)) b&1?res=mmul(res,a,p):0;
+	return res;
+}
+inline LL phi(LL x)
+{
+	LL res=x;
+	for(LL i=2;i*i<=x;i++) if(x%i==0)
+	{
+		res=res/i*(i-1);
+		while(x%i==0) x/=i;
+	}
+	if(x>1) res=res/x*(x-1);
+	return res;
+}
+LL solve()
+{
+	LL d=gcd(8,L);
+	LL v=phi(9*L/d),i;
+	for(i=1;i*i<=v;i++) if(v%i==0&&ksm(10,i,9*L/d)==1) return i;
+	i--;
+	for(;i>=1;i--) if(v%i==0&&ksm(10,v/i,9*L/d)==1) return v/i;
+	return 0;
+}
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	while(scanf("%lld",&L)==1&&L) printf("Case %d: %lld\n",++kase,solve());
+	return 0;
+}