#include<stdio.h>
int P, N, k;

int power(int x){
	if(x > N)
		return 0;
	else
		return 1 + power(x * 5);
}

int main(){
	FILE *pf, *pg;
	
	pf = fopen("fact.in", "r");
	pg = fopen("fact.out", "w");

	fscanf(pf, "%d", &P);
	N = P * 5;
	if(P == 0)
		N = 1;
	else
		if(N > 5){
			k = power(5);
			N = N - 5 * (k - 1) * k / 2;
		}	
	fprintf(pg, "%d", N);

	fclose(pf);
	fclose(pg);

	return 0;
}