#include <iostream>
#include <fstream>
using namespace std;

unsigned long long factor(int n){
    unsigned long long i=5,nr=0;
    while (n/i!=0){
        nr+=n/i;
        i *= 5;
    }
    return nr;
}


int main()
{
unsigned long long p,n,i,j,mij;
int ok=0;
fstream f,g;
f.open("fact.in",ios::in);
g.open("fact.out",ios::out);
f>>p;
i=1;
j=999999999;
while(i<j && ok==0){
        mij=(i+j)/2;
        if(factor(mij)==p)
            ok=1;
        else if(factor(mij)>p)
                j=mij-1;
        else i=mij+1;


}
if(ok==1){
while(factor(mij)==p && mij>=1){
        mij--;

}
n=mij+1;
}
else
    n=-1;

g<<n;
}