#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long p,i,k,q;
int main()
{int gasit=0;
f>>p;
if(p==0)
g<<1;
else
	for(i=5;i<=10000000&&!gasit;i+=5)
		{if(i%1220703125==0)
		    k+=13;
	 	else
			if(i%244140625==0)
				k+=12;
			else
				if(i%48828125==0)
					k+=11;
				else
					if(i%9765625==0)
						k+=10;
					else
						if(i%1953125==0)
							k+=9;
						else
							if(i%390625==0)
								k+=8;
							 else
								 if(i%78125==0)
									 k+=7;
								 else
									 if(i%15625==0)
										 k+=6;
									 else
										 if(i%3125==0)
											 k+=5;
										 else
											 if(i%625==0)
												 k+=4;
											 else
												 if(i%125==0)
													 k+=3;
												 else
													 if(i%25==0)
														 k+=2;
													 else
														 k++;
        if(k==p)
		{gasit=1;g<<i;}
		if(k>p)
		{g<<-1;gasit=1;}
		}
return 0;
}