#include <stdio.h>

int get5m(int x){
	int counter = 0;
	while(x>0){
		if(x%5)
			return counter;
		x /= 5;
		counter++;
	}
}


void swap(int &a, int &b){
	int temp;
	temp = a;
	a = b;
	b = temp;
}

int main(){
	FILE *fin = fopen("fact.in","r");
	FILE *fout = fopen("fact.out","w");
	int p,n;

	while(!feof(fin)){
		fscanf(fin,"%d", &p);
		if(!p){
			fprintf(fout, "1\n");
			continue;
		}
		n = 0;

		while(p>0){
			n += 5;
			p -=get5m(n);
		}
		fprintf(fout, "%d\n", (p==0)?n:-1);
	}

	return 0;
}