#include <fstream>
#include <cstdio>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()

{
int N,P,x=0,y=10000000,i,p=5,s=0;
in>>P;
while(x<=y - 2)
      {
       i=(x+y)/2;
       s = 0;
       p = 5;
        while(p<=i){
            s=s+i/p;
        p=p*5;
        }
        if(s<P)x=i;
        else y=i;
      }

out<<i;
    return 0;
}