求(m*10^k+x)%n即可

1 #include
     
       2 #include
      
        3 #include
       
         4 #define LL long long int 5 using namespace std; 6  7 LL rd(){ 8     LL x=0;char c=getchar();int neg=1; 9     while(c<'0'||c>'9'){
   if(c=='-') neg=-1;c=getchar();}10     while(c>='0'&&c<='9') x=x*10+c-'0',c=getchar();11     return x*neg;12 }13 14 LL modp(LL x,int k,int n){15     LL re=1;16     while(k){17         if(k&1) re=re*x%n;18         k>>=1;x=x*x%n;19     }return re;20 }21 22 int main(){23     int n=rd(),m=rd(),k=rd(),x=rd();24     printf("%d\n",(modp(10,k,n)*m+x)%n);25 }