#include <fstream.h>
#define max 1000000000;
ifstream g("fact.in");
ofstream h("fact.out");
long long b=max;
long long p;

long long f( long c )
{
     long long p = 0;
     while( c )
     {
            p += c/5;
            c /= 5;
     }
     return p;
}
void caut(long long a, long long b)
{long long m;
if(p==0) h<<1;
else{
    while (a <= b) {
        m = (a + b) / 2;
        if (f(m) <= p)
            a = m + 1;
        else
            b = m - 1;
    }
    m = (a + b) / 2;
    int ok=0;
    while(f(m) == p){
               m --;
               ok=1;}
   if(ok)    h<<++m;
   else h<<-1;
            }
}
int main(){
    g>>p;
    caut(0,b);
    return 0;
}