#include <stdio.h>
FILE *f=fopen("fact.in","r"), *g=fopen("fact.out","w");
int main()
{
long t,p,n,i=0,k5=0;
fscanf(f,"%ld",&n);
i=0;
t=0;
while (k5<n)
{
	while ((t%5==0)&&(t!=0) && (k5<n))
		{
		t/=5;
		k5++;
		}
i+=5;t=i;
}
fprintf(g,"%ld\n",i);
return 0;
}