#include<fstream.h>
int nr5=0,nr2=0;
int cautare5 (int n)
{if(n%5!=0)
	return 0;
else
	return 1+cautare5(n/5);
}
int cautare2 (int n)
{if(n%2!=0)
	return 0;
else
	return 1+cautare2(n/2);
}
void fact ( int n)
{int i,t;
for(i=1;i<=n;i++)
	{t=cautare2(i);
	nr2=nr2+t;
	t=cautare5(i);
	nr5=nr5+t;}
}
int zero (int n)
{nr2=0;
nr5=0;
fact(n);
if(nr5>nr2)
	return nr2;
else
	return nr5;
}
int b(int n, int p)
{if(p==zero(n))
	return n;
else
	if(p>zero(n))
		return b(n+1,p);
	else
		return -1;
}
int main()
{int p;
ifstream q ("fact.in");
ofstream w ("fact.out");
q>>p;
w<<b(1,p);
return 0;
}