#include <iostream>
#include <fstream>

using namespace std;

int Factorial(int n){
    int x = 5;
    int rezultat = 0;
    while(x <= n){
        rezultat += n / x;
        x *=5;
    }
    return rezultat;
}

bool Verif1(int n){
    return(n % 10 == 1 || n % 10 == 2 || n % 10 == 3 || n % 10 == 4);
}

bool Verif2(int n){
    return(n % 10 == 6 || n % 10 == 7 || n % 10 == 8 || n % 10 == 9);
}

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int p;
    f>>p;
    if(p == 0){
        g<<1;
        return 0;
    }
    int left = 1;
    int right = (1LL<<30);
    int ok = 0;
    int middle;
    while(left < right){
        middle = (left + right) >> 1;
        if(Factorial(middle) < p){
            left = middle + 1;
        }
        if(Factorial(middle) > p){
            right = middle - 1;
        }
        if(p == Factorial(middle)){
            ok = 1;
            break;
        }
    }
    if(Verif1(middle)){
        middle -= (middle % 10);
    }
    if(Verif2(middle)){
        middle = middle + 5 - (middle % 10);
    }
    while(Factorial(middle) >= p){
            --middle;
    }
    if(ok)
        g<<middle + 1;
    else
        g<<"-1";
    return 0;
}