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

long get_count(int P) {
	long count=0, i, N, tmp;
	//N = 5*P;
	i=0;
	while (i<P && count<P) {
		i++;
		count++;
		tmp = i;
		//printf("i=%ld  count=%ld   tmp = %ld\n", i, count, tmp);
		while(tmp>0 && tmp%5==0) {
			count++;
			tmp = tmp / 5;
		}
		/*
		if(count<P)
			i++;*/
	}
	if(count>P)
		return -1;
	return i*5;
}

int main(int argc, char *argv[]) {
	
	long P, N;
	
	clock_t start = clock();
	
	FILE *f1 = fopen("fact.in", "r");
	fscanf(f1, "%ld", &P);
	fclose(f1);	

	f1 = fopen("fact.out", "w");
	
	N = get_count(P);

	fprintf(f1, "%ld\n", P>0?N:1);
	fclose(f1);	
	
	printf ( "%f ms\n", ( (double)clock() - start ) * 1000 / CLOCKS_PER_SEC );
	
	return 0;
}