#include<fstream>
using namespace std;
long n,p;
ifstream f("fact.in");
ofstream g("fact.out");
long z(long x)
{long c=5,d=0;
while(c<=x)
{d+=(x/c);
c*=5;}
return d;}
long vs(long s,long d)
{if(z(s)==p)return s;
if(s<d)
{long m=(d+s)/2;
if(z(m)>=p)
return vs(s+1,m);
else return vs(m+1,d);
}return -1;}
int main()
{f>>p;g<<vs(1,int(2e9));
return 0;}