#include <fstream>
using namespace std;
int main ( )
{ ifstream f ( "fact.in");
ofstream g ( "fact.out");
int p;
f >> p;
int div2=0, div5=0, n=1;
while (div2 <p ||div5 <p)
{if (n% 2==0) div2++;
if (n% 5==0) div5++;
n++;
}
g <<n;
}