#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n,p;
    FILE *fin,*fout;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%d",&p);
    fclose(fin);
    if(p<0){
        fprintf(fout,"-1");
        return 0;
    }
    if(p==0){
        fprintf(fout,"1");
        return 0;
    }
    //if(p==0){fprintf(fout,"1");}
    n=p*5;
    while(n>4*p){
        int v=0,c=5,e=1;
        while(c<=n){
            v=v+n/c;
            c=c*5;
            e++;
        }
        if(v==p || (v<=p+e && p%(c/5)==0)){
            fprintf(fout,"%d",n);
            return 0;
        }
        n=n-5;
    }
    fprintf(fout,"%d",n);
    return 0;
}