#include<iostream>
using namespace std;

int main()
{
     int n;
    //int a = 0,b =100000000;
    FILE *in = fopen("fact.in", "r");
    FILE *out = fopen("fact.out", "w");
    fscanf(in,"%d",&n);
    unsigned int i =0;
    if(n == 0) {
        fprintf(out,"1");
    } else {
        for(i=1;n > 0;i++){
            n--;
            unsigned int ii = i;
            //cout<<ii<<" ";
            while(!(ii % 5)){
                n--;
                ii /= 5;
            }
        }
        if(n>=0)
            fprintf(out,"%d",(i-1)*5);
        else
            fprintf(out,"-1");
    }

    fclose(in);
    fclose(out);
    return 0;
}