#include <iostream>
#include <cstdio>

using namespace std;

const int L = 30;

int c, r;
int p10(int r){
    int nr=0;
    while( r >= 5  ){
            nr=nr+r/5;
            r=r/5;
        }
    return nr;
}

int main()
{
    FILE *fin, *fout;
    int n, i, pas, p;
    fin = fopen( "fact.in", "r" );
    fout = fopen( "fact.out", "w" );
    fscanf(fin, "%d", &p );
    pas = 1<<L;
    r = 0;
    while( pas > 0 ){
        if( p10(r+pas) < p )
            r = r + pas;
        pas = pas / 2;
    }
    if( r == 0 )
        fprintf( fout, "%d", -1);
    else
        fprintf( fout, "%d", r+1 );
    fclose(fin);
    fclose(fout);
    return 0;
}