#include <cstdio>

using namespace std;

typedef long long lint;

int main()
{
    lint N, M, K;
    lint S[20];
    
    scanf("%I64d %I64d %I64d", &N, &M, &K);
    
    N /= K;
    
    lint base = 9;
    for (int i = 0; i < 17; i++){
        S[i] = (i + 1) * base; base *= 10;
    }
    
    base = 10;
    
    for (int i = 0; i < 17; i++){
        if (M >= base){
            N += S[i];
        }
        else {
            N += (M - base / 10) * (i + 1);
            break;
        }
        base *= 10;
    }
    
    base = 9;
    lint A = 0;
    for (int i = 0; i < 17; i++){
        if (N >= S[i]){
            A += base;
            N -= S[i];
        }
        else {
            A += N / (i + 1);
            break;
        }
        base *= 10;
    }
    
    printf("%I64d\n", A - M + 1);
    
    return (0);
}