#include<fstream.h>
int main ()
{
	ifstream fcin("factorial.in");
	ofstream fcout("factorial.out");
	long long k,i=1,c[100001],u,p,j,i2,g,x;
		fcin>>k;
		c[i]=5;p=1;u=1;
		x=0;i=5;g=25;
		while(x<k)
			{i2=i;
				for(j=u;j>=p;j--)
				  while(i2%c[j]==0){x=x+j;i2=i2/c[j];}
			 i=i+5;
			 if(i==g){u++;c[u]=g;g=g*5;}}
	if(x==k)fcout<<i-5;
	else fcout<<-1;
	return 0;
}