#include<stdio.h>
int fact( int n){
    int f=5, put=0;
    while(n/f>=0){
        put=put+n/f;
        f=f*5;
    }
    return put;
}
int main(){
int l1,l2,pp,n,z;
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%d",&p);
l1=1;
l2=1000000000;
pp=0;
while( l1<=l2&&pp==0){
    n=(l1+l2)/2;
    z=fact(n);
    if(z==p){
        pp=1;
        n=n-n%5;
    }
    else
        if(z<p)
            l1=n+1;
        else
            l1=n-1;
}
if(pp==0)
    printf("-1");
else
    if(p==0)
        printf("1");
    else
        printf("%d",n);
return 0;
}