#include <iostream>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
#include <algorithm>
#include <cstdio>
#include <time.h>
#include <queue>
#include <set>
#include <map>
#include <stack>
#include <math.h>
//#include <bits/stdc++.h>
#define ll long long
#define int64 long long
#define mem(x,y) memset(x,y,sizeof(x))
#define ull unsigned long long
#define pb push_back
#define INF 0x7f7f7f7f
#define lson l, mid, rt<<1
#define rson mid+1, r, rt<<1|1
#define pi 3.141592653589793238462
#define stdio std::ios::sync_with_stdio(false)
#define zero(x) (((x)>0?(x):-(x))<eps)

using namespace std;

inline bool nextDouble(double &num) {
    char in;
    double Dec = 0.1;
    bool IsN = false, IsD = false;
    in = getchar();
    if (in == EOF) return false;
    while (in != '-' && in != '.' && (in < '0' || in > '9'))
        in = getchar();
    if (in == '-') {
        IsN = true;
        num = 0;
    } else if (in == '.') {
        IsD = true;
        num = 0;
    } else num = in - '0';
    if (!IsD) {
        while (in = getchar(), in >= '0' && in <= '9') {
            num *= 10;
            num += in - '0';
        }
    }
    if (in != '.') {
        if (IsN) num = -num;
        return true;
    } else {
        while (in = getchar(), in >= '0' && in <= '9') {
            num += Dec * (in - '0');
            Dec *= 0.1;
        }
    }
    if (IsN) num = -num;
    return true;
}
inline bool nextLongDouble(long double &num) {
    char in;
    long double Dec = 0.1;
    bool IsN = false, IsD = false;
    in = getchar();
    if (in == EOF) return false;
    while (in != '-' && in != '.' && (in < '0' || in > '9'))
        in = getchar();
    if (in == '-') {
        IsN = true;
        num = 0;
    } else if (in == '.') {
        IsD = true;
        num = 0;
    } else num = in - '0';
    if (!IsD) {
        while (in = getchar(), in >= '0' && in <= '9') {
            num *= 10;
            num += in - '0';
        }
    }
    if (in != '.') {
        if (IsN) num = -num;
        return true;
    } else {
        while (in = getchar(), in >= '0' && in <= '9') {
            num += Dec * (in - '0');
            Dec *= 0.1;
        }
    }
    if (IsN) num = -num;
    return true;
}
inline bool nextInt(int &num) {
    char in;
    bool IsN = false;
    in = getchar();
    if (in == EOF) return false;
    while (in != '-' && (in < '0' || in > '9')) in = getchar();
    if (in == '-') {
        IsN = true;
        num = 0;
    } else num = in - '0';
    while (in = getchar(), in >= '0' && in <= '9') {
        num *= 10, num += in - '0';
    }
    if (IsN) num = -num;
    return true;
}
inline bool nextLong(ll &num) {
    char in;
    bool IsN = false;
    in = getchar();
    if (in == EOF) return false;
    while (in != '-' && (in < '0' || in > '9')) in = getchar();
    if (in == '-') {
        IsN = true;
        num = 0;
    } else num = in - '0';
    while (in = getchar(), in >= '0' && in <= '9') {
        num *= 10, num += in - '0';
    }
    if (IsN) num = -num;
    return true;
}
inline bool blank(char ch) {
    return ch == ' ' || ch == '\n' || ch == '\r' || ch == '\t';
}
inline void read(char *s) {
    char ch = getchar();
    for (; blank(ch); ch = getchar());
    for (; !blank(ch); ch = getchar()) * s++ = ch;
    *s = 0;
}
const int maxn = 1e2 + 5;
const int maxm = 2e6 + 5;
const int mod =  1e9;
const int seed = 10007;
const double eps = 1e-6;
int a,b,x;

int main() {
    scanf("%d%d%d", &x, &a, &b);
    x-=a;
    x%=b;
    printf("%d\n",x);
    return 0;
}
/*
for(x:i) if(ans[x][j]=0) ans[i][j]=1
for(x:i) if(ans[x][j]=1)
*/
