C :

#include<stdio.h>
#include<stdlib.h>
long long ab(int k,int n)
{
    long long t,p;
    if(k==0) return 1;
    t=ab(k/2,n);
    p=(t*t)%n;
    if(k%2==0) return p;
    return (p*(10%n))%n;
}
int main()
{
    int n,m,x,k;
    long long s,q;
    while(scanf("%d%d%d%d",&n,&m,&k,&x)!=EOF)
    {
    s=ab(k,n);
    q=(x%n+(s*(m%n))%n)%n;
    printf("%lld\n",q);
    }
    return 0;
}

C++ :

#include<stdio.h>
long long ab(int k,int n)
{
     long long t;
     if(k==0)return 1;
     if(k==1)return 10%n;
     t=ab(k/2,n);
     if(k%2==0)return (t*t)%n;
     return (((t*t)%n)*(10%n))%n;
}
int main()
{
    int n,m,k,x;
    long long a;
    while(scanf("%d%d%d%d",&n,&m,&k,&x)!=EOF)
    {
    a=ab(k,n);
    printf("%lld\n",(x%n+(a*(m%n))%n)%n);
    }
return 0;
}

Pascal :

var n,m,k,x:longint;
base,t:int64; 
begin 
readln(n,m,k,x); 
base:=10; t:=1; 
while k>0 do begin
if k and 1=1 then t:=t*base mod n; 
base:=base*base mod n; 
k:=k>>1; 
end; 
writeln((x+m*t) mod n); 
end.