#include <fstream>
using namespace std;
int main(){
ifstream fi("factorial.in");
ofstream fo("factorial.out");
int a[14]={0, 10, 25, 125, 625, 3125, 15625, 78125, 390625, 1953125, 9765625, 48828125, 244140625, 1220703125}; 
int b[14]={0, 2, 6, 31, 156, 781, 3906, 19531, 97656, 488281, 2441406, 12207031, 61035156, 305175781};
int p, i, n, r;
fi>>p;
for(i=0;i<=13;i++)
  if(p<=a[i])
	break;
r=p-b[i-1];
n=a[i-1]+5*(r-1);
fo<<n;
}