#include<cstdio>
int p,n,i,j,pr,ul,mid;
FILE *f,*g;
int zfact(int n){
    int z=0,p=5;
    while(p<=n){
        z+=n/p;
        p*=5;
    }
    return z;
}

int main(){
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%d",&p);
    pr=1;
    ul=p*5;
    while(pr<=ul){
        mid=(pr+ul)/2;
        if(zfact(mid)>=p)
            ul=mid-1;
        else
            pr=mid+1;
    }
    fprintf(g,"%d\n",pr);
    fclose(f);
    fclose(g);
    return 0;
}