#include<fstream>
#include<iostream>
using namespace std;
long int n,p,b;
ifstream f("fact.in");
ofstream g("fact.out");
 
long int nrzero(long int x)
{long c=5,n5=0;
while(c<=x){n5+=(x/c);c*=5;}
return n5;
}
 
long int versol(long int ls,long int ld)
{if(nrzero(ls)==p)return ls;
if(ls<=ld){long int m=(ld+ls)/2;
if(nrzero(m)>=p)return versol(ls+1,m);
else return versol(m+1,ld);}
return -1;
}
 
int main()
{f>>p;
g<<versol(1,2000000000);
f.close();
g.close();
return 0;}