#include<stdio.h>
#include<stdlib.h>

int calc(int P)
{
	int c = P, N = 1, aux;
	while(c > 0) {
		aux = N;
		while(aux) 
			if(aux % 5 == 0){
				c--;
				aux /= 5;
			}
			else
				break;
		if(c < 0)
			return -1;
		N++;
	}				
	return N - 1;
}

int main()
{
	FILE *f = fopen("fact.in", "r");
	FILE *g = fopen("fact.out", "w");			
	int P;
	fscanf(f, "%d", &P);	
	fprintf(g, "%d", calc(P));
	fclose(f);
	fclose(g);
	exit(0);
}