#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 i, int x)
{if(x==zero(i))
	return i;
else
	if(x>zero(i))
		return b(i+1,x);
	else
		return -1;
}
int main()
{int x;
ifstream q ("fact.in");
ofstream w ("fact.out");
q>>x;
w<<b(1,x);
return 0;
}