#include<fstream.h>
#include<stdio.h>
ifstream f("fact.in");
ofstream g("fact.out");
int main(){
	long p,i=1,n,fact=1,zero=0,j;
	long v[10]={25,125,625,3125,15625,78125,390625,1953125,9765625};
	f>>p;
	while(zero<p){
		fact=fact*i;
		if(fact%10==0){
			zero++;
			if(i%5==0)
			  for(j=0;j<9;j++)
                   if(i==v[j]) 
                        zero++;					   
			fact=1;
		}
		i++;
	}
	g<<(i-1)<<"\n";
	return 0;
}