#include <bits/stdc++.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
// #define cin fin
// #define cout fout
int zerouri[100000000]; int k=0;int key; 
void zero()
    {   
        
        for(int i=0;i<=10000000;i+=5)
            {
                zerouri[k]=i/5+i/25+i/625+i/3125+i/15625+i/78125+i/390625;
                k++;
            }
    }
int binsearch(int l,int L)
    {   
        int m=(l+L)/2;
        if(m==key) return m;
        else if(key>m) return binsearch(m+1,L);
        else if(key<m) return binsearch(l,m-1);
        else return -1;

    }
int main()
    {
        zero();
        cin>>key;
        int val=binsearch(0,k-1);
        if(val!=-1) cout<<val*5;
        else cout<<val;
    }