#include <bits/stdc++.h>

using namespace std;
ifstream fin ("fact.in");
ofstream fout("fact.out");
int f(int n){
    int x=5,numere=0;
    while (x<=n){
        numere+=n/x;
        x=x*5;
    }
    return numere;
}
int main()
{
    int n;
    fin >> n;
    int st=1,dr=INT_MAX;
    while (st<dr){
        int mij=(st+dr)/2;
        if (n>f(mij))
            st=mij+1;
        else
            dr=mij;
    }
    if(f(st) == n){ 
      fout << st;
    }else 
      fout<< -1;
    
    return 0;
}