#include <stdio.h>
FILE *A, *B;
int n, i=0, factor=1 ;
long int j=1;
int main()
{
	A = fopen("fact.in", "r");
	B = fopen("fact.out", "w");
	fscanf(A, "%d", &n);
	if (n != 0)
	{
		while (i != n)
		{
			if (j % 10 == 0)
			{
				i = i + 1;
				j = j / 10;
			}
			factor = factor + 1;
			j = j*factor;
		}
		fprintf(B, "%d", factor - 1);
	}
	else
		fprintf(B, "%d", 1);
	fclose(A);
	fclose(B);
	return 0;
}