#include<cstdio>
#define MAX_RIGHT 0x7fffffff
using namespace std;

inline int f(int n)
{
    int nr, i;
    nr = 0; i = 5;
    while(n/i >= 1)
    {
        nr += n / i;
        i *= 5;
    }
    return nr;
}

int binarySearch(int x)
{
    int left = 1, right = MAX_RIGHT, mid, val;
    while(left <= right)
    {
        mid = left + (right-left)/2;
        val = f(mid);
        if(val == x)
        {
            while(f(mid-1) == x && mid-1 > 0) mid--;
            return mid;
        }
        else if(val > x)
            right = mid - 1;
        else left = mid + 1;
    }
    return -1;
}

int main()
{
    int P;
    FILE *fin, *fout;
    fin = fopen("fact.in","r");
    fout = fopen("fact.out","w");
    fscanf(fin,"%d",&P);
    fprintf(fout,"%d\n",binarySearch(P));
    fclose(fin);
    fclose(fout);
    return 0;
}