#include <iostream>
#include <cstdio>

FILE *f,*g;

using namespace std;

int main(){
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    long long P,i,V[1000];
    fscanf(f,"%lld",&P);
    V[0]=0;
    for(i=1;i<=P;i++)
    {
        V[i]=V[i-1];
        long long k=i*5;
        while(k%5==0)
        {
        V[i]++;
        k=k/5;
        }
    }
    int sem=0;
    i=0;
    while(!sem)
    {
        if(V[i]==P)
        {
            fprintf(g,"%lld",i*5);
            sem=1;
            break;
        }
        i++;
    }
    fclose(f);
    fclose(g);
    return 0;
}