#include<stdio.h>

int main()
{
	int S=0,E=0,A=0;
	scanf("%d%d%d",&S,&E,&A);
	int count=1;
	for(int i=S;i<=E;++i)
	{
		if(S==E)
		{
			printf("1\n");
			break;
		}
		if(count%10==1&&count!=1)
		{
			A-=1;
		}
		if(A==0)
		{
			printf("unsalable\n");
			break;
		}
		if(count%3==0&&count%10!=9)
		{
			S+=S/3;
		}
		else if(count%10!=9&&count%10!=0)
		{
			S+=S/10;
		}
		if(S>=E)
		{
			printf("%d\n",count+1);
			break;
		}
		count+=1;
	}
}