#include <fstream.h>
int main()
{unsigned long int p,n,a,b;
ifstream f("factorial.in");
ofstream g("factorial.out");
f>>p;n=0;a=1;b=0;
while(b!=p) {n++;a=a*n;if (a%10==0) {b++;a=a/10;}}g<<n;return 0;}