#include<fstream>
using namespace std;
int p,n,st=1,dr=500000000,mij,r=-1;
ifstream f("fact.in");
ofstream g("fact.out");
int put(int a)
{int nr=0;
while(a)
{nr+=a/5;
a/=5;
}
return nr;
}
int main()
{f>>p;
while(st<dr&&r<0)
{mij=(st+dr)/2;
n=put(mij);
if(p>n)
st=mij+1;
else if(p<=n)
{dr=mij-1;
if(p==n)
r=mij;
}
}
g<<r-(r>0)*(r%5)+(p==0);
return 0;
}