#include<iostream>#include<cmath>using namespace std;__int64 one[21],tt[30],tz[30],ones[21];__int64 mypow(__int64 a){__int64 t=1;for(int i=1;i<=a;i++)t*=10;return t;}void ini(){ __int64 f=10,w=1;one[1]=10;__int64 i;for(i=2;i<=18;i++){ w*=10;one[i]=9*w*i+one[i-1];}tt[1]=4;tz[1]=3;for(i=2;i<=18;i++){f*=10;w=(__int64)sqrt((double)f);if(w*w==f)w--;tz[i]=w;tt[i]=(w-tz[i-1])*i+tt[i-1];}}__int64 redigit1(__int64 x){__int64 j=2; if(x<=10) return x-1; for(;;j++) { if(x<=one[j]) break; } if(x==one[j]) return 9; x-=one[j-1]; __int64 u=x/j; __int64 s=mypow(j-1)+u-1; if(u*j==x) return s%10; s++; x-=u*j; s/=mypow(j-x); return s%10;}__int64 redigit2(__int64 x){if(x<=4)return (x-1)*(x-1);int j=2;while(x>tt[j]) j++;if(x==tt[j])return (tz[j]*tz[j])%10;x-=tt[j-1];__int64 p=x/j;__int64 y;x-=j*p;__int64 o=tz[j-1]+p;if(x==0)return (o*o)%10; o++; o*=o; o/=mypow(j-x); return o%10;}int main(){__int64 k,a,b,jin,ss,a1,a2;ini();while(scanf("%I64d",&k)&&k){ k++; a=redigit1(k);b=redigit2(k);a1=redigit1(k+1);a2=redigit2(k+1);jin=0;while(a1+a2>8){if(a1+a2>=10) { jin=1; break; } k++; a1=redigit1(k+1);a2=redigit2(k+1);}printf("%I64dn",(a+b+jin)%10);}return 0;}
