#include "stdio.h"

int get5(int n){
	int ret=0;
	while(n%5==0){
		n = n/5;
		ret++;
	}
	return ret;
}
int fact_zeros(int n){
	int i=1;
	int fvs=0;
	int ok=0;
	while(!ok){
		fvs += get5(i);
		if(fvs==n)
			return i;
		if(fvs>n)
			return -1;
		i++;
	}
	return -1;
}

int main(){
	int x;
	int rez;

	FILE *f,*g;
	f = fopen("fact.in","r");
	g = fopen("fact.out","w");
	
	fscanf(f,"%d",&x);
	fprintf(g,"%d",fact_zeros(x));

	return 0;
}