#include<iostream>
#include<fstream.h>
long int p;
long long fact(int n) {
	if(n==1) return 1;
	else if(n>1) return n*fact(n-1);
}
int nrZerouri(long long x) {
	int nrzero=0;
	while(x!=0 && x%10==0) {
		nrzero++;
		x=x/10;
	}
	return nrzero;
}
int main() {
	int gasit=0,i=1;
	ifstream f("fact.in");f>>p;
	
	while(!gasit) {
		if(nrZerouri(fact(i))==p) gasit++;
		else if(nrZerouri(fact(i))>p) {
			i=-1;
			break;
		}
		else i++;
	}
	if(i==0) cout<<"nu exista";
	ofstream g("fact.out");
	g<<i;
	f.close();
	g.close;
}